#include <bits/stdc++.h>
using namespace std;
long long n;
long long m;
vector<pair<long long, long long> > g[505];
long long vis[505];
long long parentedge[505];
long long U[500005], V[500005];
vector<long long> store;
vector<pair<long long, long long> > edges;
bool findloop(long long u, long long edgeidx) {
  if (vis[u] == 1) {
    store.push_back(edgeidx);
    long long src = U[edgeidx];
    while (src != u) {
      long long eidx = parentedge[src];
      store.push_back(eidx);
      src = U[eidx];
    }
    return 1;
  }
  if (vis[u] == 2) return 0;
  vis[u] = 1;
  parentedge[u] = edgeidx;
  for (auto v : g[u]) {
    if (findloop(v.first, v.second)) return 1;
  }
  vis[u] = 2;
  return 0;
}
bool checkloop() {
  for (long long i = 1; i <= n; i++) {
    if (!vis[i] && findloop(i, -1)) return 1;
  }
  return 0;
}
bool findloop2(long long u, long long removed) {
  if (vis[u] == 1) return 1;
  if (vis[u] == 2) return 0;
  vis[u] = 1;
  for (auto it : g[u]) {
    if (it.second == removed) continue;
    if (findloop2(it.first, removed)) return 1;
  }
  vis[u] = 2;
  return 0;
}
bool checkloop2(long long removed) {
  fill(vis + 1, vis + n + 1, 0);
  for (long long i = 1; i <= n; i++) {
    if (!vis[i] && findloop2(i, removed)) return 0;
  }
  return 1;
}
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> n;
  cin >> m;
  for (long long i = 1; i <= m; i++) {
    long long x, y;
    cin >> x >> y;
    U[i] = x;
    V[i] = y;
    g[x].push_back({y, i});
  }
  if (!checkloop())
    cout << "YES\n";
  else {
    for (auto it : store) {
      if (checkloop2(it)) {
        cout << "YES\n";
        return 0;
      }
    }
    cout << "NO\n";
  }
  return 0;
}
