fn.cpp

#include<iostream>
 
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<math.h>
 
#include<vector>
 
using namespace std;
 
#define FOR(i,a,b) for(int i=a; i<=b; i++)
 
#define PII pair<int, int>
#define MP make_pair
#define PB push_back
 
#define SIZE(s) (int)(s).int()
 
#define ll long long
 
#define MAX 10047
 
int V[MAX];
int N, M;
 
int main()
{
	int a, b;
	while(scanf("%d %d",&N, &M)== 2)
	{
		FOR(i,0,N-1) V[i] = 0;
		while(M--)
		{
			scanf("%d %d",&a,&b);
			a--; b--;
			V[a]++;
			V[b]++;
		}
 
		bool ok = false;
		FOR(i,0,N-1)
		{
			if (V[i] >= 4) ok = true;
		}
 
		if (ok) puts("YES");
		else puts("NO");
	}
	return 0;
}