#include <iostream>
#include <vector>
#include <set>
using namespace std;
const int N=20000;
int n;
vector<int> edge[N];
bool flag[N][N];
void dfs(int p,int cur,int d){
	if(d==3){
		flag[p][cur]=true;
		return;
	}
	for(int i=0;i<edge[cur].size();i++){
		if(edge[cur][i]==p)	continue;
		dfs(cur,edge[cur][i],d+1);
	}
	return;
}
int main(){
	int m;	cin>>n>>m;
	for(int i=0;i<n;i++){
		int a,b;	cin>>a>>b;	a--;	b--;
		edge[a].push_back(b);
		edge[b].push_back(a);
	}
	dfs(0,0,0);
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			if(flag[i][j]&&flag[j][i]){
				cout<<"YES"<<endl;
				return 0;
			}
		}
	}
	cout<<"NO"<<endl;
	return 0;
}