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;
}