#include <cstdio>
#include <cstring>
#include <string>
#include <cmath>
#include <cassert>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <set>
#include <map>
#include <bitset>
using namespace std;

#define repl(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define rep(i,n) repl(i,0,n)
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define all(x) (x).begin(),(x).end()
#define dbg(x) cout<<#x"="<<x<<endl
#define fi first
#define se second

#define INF 2147483600

#define N 20000
vector<int> g[N];
bool  visited[N];
bool memo[4][N];

bool dfs(int f, int d){
  if(d>0 && !memo[d-1][f]) return false;
  memo[d][f]=false;

  if(d==4){
    rep(i,g[f].size()) if(g[f][i]==1) return true;
    return false;
  }
  visited[f]=true;
  rep(i,g[f].size()) if(!visited[g[f][i]] && dfs(g[f][i], d+1)) return true;
  visited[f]=false;
  return false;
}

int main(){
  int n,m;
  cin>>n>>m;
  rep(i,m){
    int a,b;
    scanf("%d %d", &a, &b);
    a--;b--;
    g[a].pb(b);
    g[b].pb(a);
  }

  fill(visited, visited+N, false);
  fill(memo[0], memo[4], true);

  if(dfs(0,0)){
    cout<<"YES"<<endl;
    return 0;
  }

  cout<<"NO"<<endl;
  return 0;
}