#include <iostream>
#include <algorithm>
#include <vector>
#include <utility>
#include <set>
#include <map>
using namespace std;

vector<set<int>> v(2000);
int was[2000];


bool dfs(int x) {
	was[x] = 1;
	for (auto y : v[x]) {

		if (!was[y]) {
			dfs(y);
		}
		else {
			return 1;
		}
	}
	return 0;
}

int main() {


	int n, m;
	cin >> n >> m;


	for (int i = 0; i < m; i++) {
		int a, b;
		cin >> a >> b;
		v[a].insert(b);
		v[b].insert(a);
	}

	for (int i = 1; i <= n; i++) {
		for (int i = 1; i <= n; i++) {
			was[i] = 0;
		}
		if (dfs(i)) {
			cout << "YES";
			return 0;
		}
	}
	cout << "NO";
	return 0;
}