fn.cpp

 
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cmath>
 
using namespace std;
 
int main() {
	int n, m;
	while (scanf("%d %d", &n, &m) == 2) {
		bool bunny = false;
		int *paws = new int[n];
		memset(paws, 0, n*sizeof(int));
		for (int i = 0; i < m; i++) {
			int x, y;
			scanf("%d %d", &x, &y);
			x--, y--;
			paws[x]++;
			paws[y]++;
			if (paws[x] == 4) bunny = true;
			if (paws[y] == 4) bunny = true;
		}
		printf(bunny ? "YES\n" : "NO\n");
	}
	return 0;
}