This solution is giving wrong answer in 3 test cases which are very large and i am unable to debug those Please Help....;)

bool dfs(int node, vector<int> adj[], int vis[], int par, stack<int> &st) {
	vis[node] = 1;
	st.push(node);
	for (auto x : adj[node]) {
		if (!vis[x]) {
			if (dfs(x, adj, vis, node, st)) {
				return true;
			}
		}
		else if (x != par) {
			st.push(x);
			return true;
		}
	}
	return false;
}

int main()
{
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
	int n, m;
	cin >> n >> m;
	vector<int> adj[n + 1];
	for (int i = 0; i < m; i++) {
		int x, y;
		cin >> x >> y;
		adj[x].pb(y);
		adj[y].pb(x);
	}
	stack<int> st;
	int vis[n + 1] = {0};
	int fl = 0;;
	for (int i = 1; i <= n; i++) {
		if (!vis[i]) {
			if (dfs(i, adj, vis, -1, st)) {
				fl++;
				break;
			}
		}
	}
	if (fl) {
		vector<int> ans;
		int x = st.top();
		ans.pb(x);
		st.pop();
		while (st.size() > 0 && st.top() != x) {
			ans.pb(st.top());
			st.pop();
		}
		ans.pb(x);
		cout << ans.size() << endl;
		for (auto x : ans)
			cout << x << " ";
	}
	else
		cout << "IMPOSSIBLE";
}