fn.cpp

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <algorithm>
#include <utility>
#include <string>
#include <deque>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <vector>
using namespace std;
 
#define debug printf
//#define debug blackhole
void blackhole(...) {}
 
#define MAXN 1400
int ADJACENT[MAXN][MAXN];
int ADJ_N[MAXN];
int V;
int E;
 
void GO() {
	for (int i=0;i<MAXN;i++) {
		ADJ_N[i]=0;
	}
	for (int i = 0; i < E; i++) {
		int a, b;
		scanf("%d%d", &a, &b);
		ADJACENT[a][ADJ_N[a]] = b;
		ADJ_N[a]++;
		ADJACENT[b][ADJ_N[b]] = a;
		ADJ_N[b]++;
	}
 
	int qq;
	for (qq=0;qq<V;qq++) {
		if (ADJ_N[qq] >= 4){
			printf("YES\n");
			break;
		}
	}
	if (qq==V) printf("NO\n");
}
 
int main() {
	while (true) {
		if (scanf("%d%d", &V, &E) != 2) break;
		GO();
	}
	return 0;
}