fn.cpp

#include <iostream>
#include <vector>
#include <cstdio>
#include <cmath>
#include <set>
#include <map>
#include <string>
 
using namespace std;
 
int main()
{
	vector< vector<int> > G;
	vector< int > C;
	int N, M;
	while(scanf("%d %d", &N, &M) == 2)
	{
		G = vector< vector<int> >(N);
		C = vector< int >(N);
		for(int i=0; i<N; i++)
		{
			G[i] = vector<int>();
			C[i] = 0;
		}
		for(int i=0; i<M; i++)
		{
			int x, y;
			scanf("%d %d", &x, &y);
			--x;
			--y;
			G[x].push_back(y);
			G[y].push_back(x);
			C[x]++;
			C[y]++;
		}
		bool ok = false;
		for(int i=0; i<N; i++)
		{
			if(C[i] >= 4)
			{
				puts("YES");
				ok = true;
				break;
			}
		}
		if(!ok)
			puts("NO");
	}
 
	return 0;	
}