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#include <bits/stdc++.h>
 
 
#pragma GCC optimize("Ofast,fast-math,unroll-loops")
#pragma GCC target("avx2,fma")
using namespace std;
#define ll long long
#define int ll
#define all(a) a.begin(),a.end()
#define allr(a) a.rbegin(),a.rend()
#define pb push_back
#define yes cout<<"YES"
#define no cout<<"NO"
#define endl '\n'
#define endll cout<<endl
#define Fast ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
#define F first
#define S second
#define im cout<<"IMPOSSIBLE"
const int N = 5e5 + 11;
const int NN = 106;
const int mo = 1e9 + 123;
const int mod = 1e9 + 7;
const int m = 1e9 + 123;
const int Mod = 998244353;
const ll inf = 1e18;
const int LOG = 19;
#define PI 3.14159265
 
 
int Lcm(int x, int y) {
    return x / __gcd(x, y) * y;
}
 
vector<int> v[N];
int vis[N];
 
void dfs(int node) {
    vis[node] = 1;
    for (auto i: v[node]) {
        if (vis[i])continue;
        dfs(i);
    }
}
 
void solve() {
    int n, m;
    cin >> n >> m;
    for (int i = 0; i < m; ++i) {
        int x, y;
        cin >> x >> y;
        v[x].pb(y);
        v[y].pb(x);
    }
    int cnt = 0;
    vector<int> ans;
    for (int i = 1; i <= n; i++) {
        if (vis[i])
            continue;
        dfs(i);
        cnt++;
        ans.pb(i);
    }
    cout << cnt - 1 << endl;
    for (int i = 1; i < ans.size(); ++i) {
        cout << ans[0] << " " << ans[i] << endl;
    }
 
}
 
 
int32_t main() {
    Fast;
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    int t = 1;
    //cin >> t;
    for (int i = 1; i < t + 1; ++i) {
        // cout << "Case #" << i << ": ";
        solve();
    }
    return 0;
}

Main.java:1: error: illegal character: '#'
#include <bits/stdc++.h>
^
Main.java:1: error: class, interface, or enum expected
#include <bits/stdc++.h>
         ^
Main.java:4: error: illegal character: '#'
#pragma GCC optimize("Ofast,fast-math,unroll-loops")
^
Main.java:5: error: illegal character: '#'
#pragma GCC target("avx2,fma")
^
Main.java:7: error: illegal character: '#'
#define ll long long
^
Main.java:7: error: class, interface, or enum expected
#define ll long long
        ^
Main.java:8: error: illegal character: '#'
#define int ll
^
Main.java:9: error: illegal character: '#'
#define all(a) a.begin(),a.end()
^
Main.java:10: error: illegal character: '#'
#define allr(a) a.rbegin(),a.rend()
^
Main.java:11: error: illegal character: '#'
#define pb push_back
^
Main.java:12: error: illegal character: '#'
#define yes cout<<"YES"
^
Main.java:13: error: illegal character: '#'
#define no cout<<"NO"
^
Main.java:14: error: illegal character: '#'
#define endl '\n'
^
Main.java:15: error: illegal character: '#'
#define endll cout<<endl
^
Main.java:16: error: illegal character: '#'
#define Fast ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
^
Main.java:16: error: class, interface, or enum expected
#define Fast ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
                                              ^
Main.java:16: error: class, interface, or enum expected
#define Fast ios_base::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
                                                               ^
Main.java:17: error: illegal character: '#'
#define F first
^
Main.java:17: error: class, interface, or enum expected
#define F first
        ^
Main.java:18: error: illegal character: '#'
#define S second
^
Main.java:19: error: illegal character: '#'
#define im cout<<"IMPOSSIBLE"
^
Main.java:21: error: class, interface, or enum expected
const int NN = 106;
^
Main.java:22: error: class, interface, or enum expected
const int mo = 1e9 + 123;
^
Main.java:23: error: class, interface, or enum expected
const int mod = 1e9 + 7;
^
Main.java:24: error: class, interface, or enum expected
const int m = 1e9 + 123;
^
Main.java:25: error: class, interface, or enum expected
const int Mod = 998244353;
^
Main.java:26: error: class, interface, or enum expected
const ll inf = 1e18;
^
Main.java:27: error: class, interface, or enum expected
const int LOG = 19;
^
Main.java:28: error: illegal character: '#'
#define PI 3.14159265
^
Main.java:28: error: class, interface, or enum expected
#define PI 3.14159265
        ^
Main.java:33: error: class, interface, or enum expected
}
^
Main.java:36: error: class, interface, or enum expected
int vis[N];
^
Main.java:38: error: class, interface, or enum expected
void dfs(int node) {
^
Main.java:40: error: class, interface, or enum expected
    for (auto i: v[node]) {
    ^
Main.java:42: error: class, interface, or enum expected
        dfs(i);
        ^
Main.java:43: error: class, interface, or enum expected
    }
    ^
Main.java:48: error: class, interface, or enum expected
    cin >> n >> m;
    ^
Main.java:49: error: class, interface, or enum expected
    for (int i = 0; i < m; ++i) {
    ^
Main.java:49: error: class, interface, or enum expected
    for (int i = 0; i < m; ++i) {
                    ^
Main.java:49: error: class, interface, or enum expected
    for (int i = 0; i < m; ++i) {
                           ^
Main.java:51: error: class, interface, or enum expected
        cin >> x >> y;
        ^
Main.java:52: error: class, interface, or enum expected
        v[x].pb(y);
        ^
Main.java:53: error: class, interface, or enum expected
        v[y].pb(x);
        ^
Main.java:54: error: class, interface, or enum expected
    }
    ^
Main.java:56: error: class, interface, or enum expected
    vector<int> ans;
    ^
Main.java:57: error: class, interface, or enum expected
    for (int i = 1; i <= n; i++) {
    ^
Main.java:57: error: class, interface, or enum expected
    for (int i = 1; i <= n; i++) {
                    ^
Main.java:57: error: class, interface, or enum expected
    for (int i = 1; i <= n; i++) {
                            ^
Main.java:60: error: class, interface, or enum expected
        dfs(i);
        ^
Main.java:61: error: class, interface, or enum expected
        cnt++;
        ^
Main.java:62: error: class, interface, or enum expected
        ans.pb(i);
        ^
Main.java:63: error: class, interface, or enum expected
    }
    ^
Main.java:65: error: class, interface, or enum expected
    for (int i = 1; i < ans.size(); ++i) {
    ^
Main.java:65: error: class, interface, or enum expected
    for (int i = 1; i < ans.size(); ++i) {
                    ^
Main.java:65: error: class, interface, or enum expected
    for (int i = 1; i < ans.size(); ++i) {
                                    ^
Main.java:67: error: class, interface, or enum expected
    }
    ^
Main.java:74: error: illegal character: '#'
#ifndef ONLINE_JUDGE
^
Main.java:74: error: class, interface, or enum expected
#ifndef ONLINE_JUDGE
        ^
Main.java:76: error: class, interface, or enum expected
    freopen("output.txt", "w", stdout);
    ^
Main.java:77: error: illegal character: '#'
#endif
^
Main.java:78: error: class, interface, or enum expected
    int t = 1;
    ^
Main.java:80: error: class, interface, or enum expected
    for (int i = 1; i < t + 1; ++i) {
    ^
Main.java:80: error: class, interface, or enum expected
    for (int i = 1; i < t + 1; ++i) {
                    ^
Main.java:80: error: class, interface, or enum expected
    for (int i = 1; i < t + 1; ++i) {
                               ^
Main.java:83: error: class, interface, or enum expected
    }
    ^
Main.java:85: error: class, interface, or enum expected
}
^
66 errors

Standard output is empty