#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <stack>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

int depth[20005];
vector<int> v[20005];
int visit[5];

bool ret;

void dfs(int idx){
  if(ret) return;
  if(idx == 4){
    rep(i,v[visit[4]].size()){
      if(v[visit[4]][i] == 1){
        ret = true;
        //cout << visit[0] << " " << visit[1] << " " << visit[2] << " " << visit[3] << " " << visit[4] << endl;
        return;
      }
    }
    return;
  }
  map<int,int> memo;
  rep(i,idx+1) memo[visit[i]] = 1;
  rep(i,v[visit[idx]].size()){
    int nxt = v[visit[idx]][i];
    if(memo.count(nxt) == 0){
      visit[idx+1] = nxt;
      dfs(idx+1);
    }
  }
}

int main(){
  ios::sync_with_stdio(false);
  int N, M;
  cin >> N >> M;
  rep(i,M){
    int a, b;
    cin >> a >> b;
    v[a].push_back(b);
    v[b].push_back(a);
  }

  ret = false;
  
  visit[0] = 1;
  dfs(0);

  if(ret) cout << "YES" << endl;
  else cout << "NO" << endl;
  
  return 0;
}