#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)

int n, m;
// vector<int> g[20001];
bool memo[20001][20001];

int main(void){
    cin >> n >> m;
    rep(i, m){
        int a, b; scanf("%d %d", &a, &b);
        a--; b--;
        // g[a].push_back(b);
        // g[b].push_back(a);
        memo[a][b] = memo[b][a] = true;
    }

    /*

    //1 - u - vとなるような辺を見つける
    vector<pair<int, int> > d;
    for(int u : g[0]){
        for (int v : g[u]){
            //頂点に戻るようなものは入れない
            if(v != 0) d.push_back(make_pair(u, v));
        }
    }

    */
    vector<pair<int, int> > d;
    for (int u = 1; u < n; ++u){
        if(memo[0][u]){
            for (int v = 0; v < n; ++v){
                if(memo[u][v]){
                    d.push_back(make_pair(u, v));
                }
            }
        }
    }

    for (int i = 0; i < d.size() - 1; ++i){
        for (int j = i + 1; j < d.size(); ++j){
            if(d[i].first  != d[j].first && d[i].first  != d[j].second && 
               d[i].second != d[j].first && d[i].second != d[j].second){
                
                if(memo[d[i].second][d[j].second]){
                    printf("YES\n");
                    return 0;
                }
                
            }
        }
    }
    printf("NO\n");
    return 0;
}