fn.cpp

#include <cstdio>
#include <cstdlib>
#include <cmath>
 
#include <string>
#include <vector>
#include <iostream>
 
using namespace std;
 
const static int MAX = 10050;
int poi[MAX];
 
 
bool load()
{
    int points, lines;
    bool bunny = false;
 
    if (scanf("%d%d", &points, &lines) != 2)
        return false;
 
    for(int i=0; i<MAX; i++)
	poi[i] = 0;
 
    for (int i = 0; i < lines; ++i) 
    {
	int from, to;
        scanf("%d%d", &from, &to);
	poi[from]++;
	poi[to]++;
	if(poi[from] >=4 || poi[to] >=4)
		bunny = true;
 
    }
    if(bunny)
	cout << "YES" << endl;
    else
	cout << "NO" << endl;
    return true;
}
 
int main()
{
    while (load()) {}
    return 0;
}