3987. Complete Graph

#include <bits/stdc++.h>

using namespace std;

#define int long long
#define mp make_pair
#define pb push_back

const int N = 101;

bool bridge[N][N];

signed main() {
    ios::sync_with_stdio(0);cin.tie(nullptr);cout.tie(nullptr);
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);

    int n,m;
    cin >> n >> m;

    int sum = 0;

    for(int i=0,a,b;i<m;i++)
    {
        cin >> a >> b;
        sum += !bridge[a][b];
        bridge[a][b] = 1;
        bridge[b][a] = 1;
    }

    cout << (sum == n*(n-1)/2 ? "YES" : "NO");

    return 0;
}