//#pragma GCC optimize("O3", "unroll-loops")
//#pragma GCC target("avx2", "bmi", "bmi2", "lzcnt", "popcnt")
 
#include <bits/stdc++.h>
#define ldb long double
//#define double ldb
#define db double
#define unomap unordered_map
#define unoset unordered_set
#define endl '\n'
#define str string
#define strstr stringstream
#define sz(a) (int)a.size()
#define ll long long
//#define int ll
#define pii pair <int, int>
#define pll pair <ll, ll>
#define Unique(a) a.resize(unique(all(a)) - a.begin())
#define ull unsigned ll
#define fir first
#define sec second
#define idc cin.ignore()
#define lb lower_bound
#define ub upper_bound
#define all(s) s.begin(), s.end()
#define rev reverse
#define gcd __gcd
#define pushb push_back
#define popb pop_back
#define pushf push_front
#define popf pop_front
#define mul2x(a, x) a << x
#define div2x(a, x) a >> x
#define lcm(a, b) (a / __gcd(a, b) * b)
#define log_base(x, base) log(x) / log(base)
#define debug cerr << "No errors!"; exit(0);
#define forw(i, a, b) for (int i = a; i <= b; ++i)
#define forw2(i, a, b) for (ll i = a; i <= b; ++i)
#define fors(i, a, b) for (int i = a; i >= b; --i)
#define fors2(i, a, b) for (ll i = a; i >= b; --i)
#define pqueue priority_queue
#define sqrt sqrtl
#define i128 __int128
#define popcount __builtin_popcountll
#define BIT(x, i) (((x) >> (i)) & 1)
#define MASK(x) ((1LL) << (x))
#define want_digit(x) cout << fixed << setprecision(x);
#define excuting_time 1000.0 * clock() / CLOCKS_PER_SEC
using namespace std;
const int MOD = 1e9 + 7; // 998244353
const int inf = 1e9;
const ll INF = 1e18;
const int N = 5e3;
 
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll random(const ll &L, const ll &R) {
    return uniform_int_distribution<ll> (L, R) (rng);
}
 
int n, m, u, v, par[N + 5], sz[N + 5];
unomap <int, int> cnt;
 
struct DSU {
    int find(int v) {
        return v == par[v] ? v : par[v] = find(par[v]);
    }
 
    void join(int a, int b) {
        a = find(a);
        b = find(b);
        if (a != b) par[b] = a;
    }
} dsu;
 
void solve() {
    cin >> n >> m;
    forw (i, 1, n) par[i] = i;
    while (m--) {
        cin >> u >> v;
        dsu.join(u, v);
    }
 
    forw (i, 1, n) ++cnt[dsu.find(i)];
    cout << sz(cnt) - 1 << endl;
    vector <int> v;
    for (pii tmp : cnt) v.pushb(tmp.fir);
    forw (i, 1, sz(v) - 1) cout << v[0] << ' ' << v[i] << endl;
}
 
signed main() {
    ios::sync_with_stdio(false), cin.tie(nullptr);
    srand(time(NULL));
    #define name "COMNET"
    if (fopen(name".INP", "r")) {
        freopen(name".INP", "r", stdin);
        freopen(name".OUT", "w", stdout);
    }
    bool testCase = false;
    int numTest = 1;
//    cin >> numTest;
    forw (i, 1, numTest) {
        if (testCase) cout << "Case " << i << ": ";
        solve();
    }
    return 0;
}