#include <bits/stdc++.h> 
 
using namespace std;  
 
typedef long long ll;  
typedef pair<int, int> ii;  
 
const int INF = 1e9;  
const ll LINF = 1e18;  
 
const int N = 1e5 + 5; 
 
// Để kiểm tra một đồ thị vô hướng có tồn tại chu trình hay không
// thì ta kiểm tra có tồn tại cạnh ngược trong cây dfs hay không
int n, m;  
vector<int> adj[N]; 
 
bool vis[N]; 
int p[N]; // p[u] là đỉnh cha của u trên cây dfs
int cycle_start, cycle_end; 
 
void dfs(int u) {
	vis[u] = true;  
	for (int v : adj[u]) {
		if (v == p[u]) continue;  
		if (!vis[v]) {
			// (u, v) là cạnh của cây dfs (cạnh nét liền)
			p[v] = u; 
			dfs(v); 
		}
		else {
			// (u, v) là cạnh ngược (cạnh nét đứt)
			if (cycle_start == -1) {
				cycle_start = v;  
				cycle_end = u;  
			}
		}
	}
}
 
int main() {
	ios::sync_with_stdio(false); 
	cin.tie(nullptr); 	
	cin >> n >> m; 
 
	for (int i = 0; i < m; i++) {
		int u, v; 
		cin >> u >> v; 
		adj[u].push_back(v); 
		adj[v].push_back(u); 
	}
 
	cycle_start = -1; 
	for (int u = 1; u <= n; u++) {
		if (!vis[u]) dfs(u); 
	}
 
	if (cycle_start == -1) {
		cout << "IMPOSSIBLE"; 
	}
	else {
		vector<int> cycle; 
		int t = cycle_end;  
		while (true) {
			cycle.push_back(t);  
			if (t == cycle_start) break;
			t = p[t];  
		}
		reverse(cycle.begin(), cycle.end());  
		cycle.push_back(cycle_start);  
 
		cout << cycle.size() << '\n'; 
		for (int u : cycle) cout << u << ' '; 
	}
}

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5 6
1 3
1 2
5 3
1 5
2 4
4 5