//TLE
#include <iostream>
#include <vector>
using namespace std;

int n, m;
vector<int> et[20001];
bool used[20001] = {false};

bool dfs(int u, int dep) {
	used[u] = true;
	
	if (dep == 4) {
		for (int i = 0; i < et[u].size(); i++) {
			if (et[u][i] == 1) return true;
		}
		return false;
	}
	
	for (int i = 0; i < et[u].size(); i++) {
		int v = et[u][i];
		if (used[v]) continue;
		if (dfs(v, dep + 1)) return true;
	}
	return false;
}

int main() {
	int i;
	
	cin >> n >> m;
	for (i = 0; i < m; i++) {
		int u, v;
		cin >> u >> v;
		et[u].push_back(v);
		et[v].push_back(u);
	}
	if (dfs(1, 0)) cout << "YES" << endl;
	else cout << "NO" << endl;
	return 0;
}