https://codeforces.com/problemset/problem/1169/B?csrf_token=5b9156034386ea79799008822cac92c7

Pairs.cpp

#include <bits/stdc++.h>
using namespace std;

vector<pair<int,int> > vpairs; 

int main()
{
  //write your code here
  int n,m;
  cin>>n>>m;
  while(m--)
  {
    int a,b;
    cin>>a>>b;
    vpairs.emplace_back(a,b);
  }
  
  for(int x: {vpairs[0].first,vpairs[0].second})
  {
    vector<int> val(n+1);
    int all = 0;
    for(auto c: vpairs)
    {
      if(c.first != x && c.second != x)
      {
        val[c.first]++;
        val[c.second]++;
        all++;
      }
    }
    if(*max_element(val.begin(),val.end()) == all)
    {
      cout<<"YES\n";
      return 0;
    }
  }
  cout<<"NO\n";
  return 0;
}