#include <bits/stdc++.h>
using namespace std;
const int N = 150005;
int n, m;
int a, b;
vector<int> g[N];
bool pos[N];
vector<int> dsu;
bool rez;
bool proveri() {
  for (int u = 0; u < dsu.size(); u++)
    if (g[dsu[u]].size() != dsu.size() - 1) return false;
  return true;
}
void dfs(int cvor) {
  pos[cvor] = true;
  dsu.push_back(cvor);
  for (int v = 0; v < g[cvor].size(); v++)
    if (!pos[g[cvor][v]]) dfs(g[cvor][v]);
}
void DFS() {
  for (int u = 1; u <= n && !rez; u++) {
    if (!pos[u]) {
      dsu.clear();
      dfs(u);
      if (!proveri()) rez = true;
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    cin >> a >> b;
    g[a].push_back(b);
    g[b].push_back(a);
  }
  DFS();
  if (rez == true)
    cout << "NO" << endl;
  else
    cout << "YES" << endl;
  return 0;
}
