#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <set>

using namespace std;

const int INF = 99;
vector<vector<int>> connect_v;
vector<set<int>> connect_s;

template <class T>
void show(T t) {
	for (auto e : t) {
		cout << e << " ";
	}
	cout << endl;
}

// v[0, b, c, d, e]
bool dfs(vector<int> &v, int idx) {
	// printf("%d: ", idx);
	// show(v);
	int now = v[idx];
	if (idx == 4) {
		return connect_s[now].count(0) > 0;
	}

	for (auto next : connect_v[now]) {
		if (find(v.begin(), v.end(), next) != v.end()) {
			continue;
		}
		v[idx + 1] = next;
		if (dfs(v, idx + 1)) {
			return true;
		}
		v[idx + 1] = -1;
	}

	return false;
}

int main() {
	int n, m, a, b;

	scanf("%d %d", &n, &m);
	connect_v.assign(n, vector<int>());
	connect_s.assign(n, set<int>());
	for (int i = 0; i < m; i++) {
		scanf("%d %d", &a, &b);
		a--;
		b--;
		connect_v[a].emplace_back(b);
		connect_v[b].emplace_back(a);
		connect_s[a].insert(b);
		connect_s[b].insert(a);
	}

	// for (int i = 0; i < 5; i++) {
	// 	printf("%d: ", i);
	// 	show(connect_s[i]);
	// }

	vector<int> points(5, -1);
	points[0] = 0;
	bool ret = dfs(points, 0);

	if (ret) {
		printf("YES\n");
	} else {
		printf("NO\n");
	}
	return 0;
}