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;
}