#include <bits/stdc++.h>
using namespace std;
const int N = 505;
int n, m, foundCycle = 0, esv, cec = 0, mode = 1;
set<int> g[N];
vector<pair<int, int>> cel;
stack<int> fcs;
char vis[N];
void fc(int u) {
  vis[u] = 1;
  if (mode) fcs.push(u);
  for (int v : g[u]) {
    if (vis[v] == 0)
      fc(v);
    else if (vis[v] == 1) {
      foundCycle = 1, esv = v;
      return;
    }
    if (foundCycle) return;
  }
  vis[u] = 2;
  if (mode) fcs.pop();
}
int main() {
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int u, v;
    cin >> u >> v;
    g[u].insert(v);
  }
  for (int i = 1; i <= n; i++)
    if (vis[i] == 0 && !foundCycle) fc(i);
  if (!foundCycle) {
    cout << "YES" << endl;
    return 0;
  }
  int tprev = esv;
  while (fcs.top() != esv) {
    int u = fcs.top();
    fcs.pop();
    cel.push_back({u, tprev});
    tprev = u;
  }
  cel.push_back({esv, tprev});
  mode = 0;
  for (auto e : cel) {
    g[e.first].erase(e.second);
    foundCycle = 0, memset(vis, 0, sizeof(vis));
    for (int i = 1; i <= n; i++)
      if (vis[i] == 0 && !foundCycle) fc(i);
    if (!foundCycle) {
      cout << "YES" << endl;
      return 0;
    }
    g[e.first].insert(e.second);
  }
  cout << "NO" << endl;
  return 0;
}
