#include <cstdio> #include <vector> #include <iostream> #include <string> #include <algorithm> #include <cstring> #include <set> #include <vector> using namespace std; int main() { int N,M,x,y,i; int p[10001]; while (scanf("%d %d\n",&N,&M) > 0) { for(i=0;i<=10000;i++) p[i]=0; for(i=1;i<=M;i++) { scanf("%d %d\n",&x,&y); p[x]++; p[y]++; if (p[x]==4 || p[y] == 4) break; } if (p[x]==4 || p[y] == 4) printf("YES\n"); else printf("NO\n"); } return 0; }