#include <bits/stdc++.h>
using namespace std;
const int MAXN = 500;
const int MAXM = (int)1e5;
vector<int> g[MAXN + 1];
int x[MAXM + 1], y[MAXM + 1];
int ok[MAXN + 1];
bool flag;
vector<int> edge;
void dfs(int nod) {
  ok[nod] = 1;
  edge.push_back(nod);
  for (auto it : g[nod]) {
    if (flag == 0) {
      if (ok[it] == 0) {
        dfs(it);
      } else if (ok[it] == 1) {
        flag = 1;
        edge.push_back(it);
      }
    }
  }
  ok[nod] = 2;
  if (flag == 0) edge.pop_back();
}
int a, b;
void dfs1(int nod) {
  ok[nod] = 1;
  for (auto it : g[nod]) {
    if (flag == 0 && !(a == nod && b == it)) {
      if (ok[it] == 0) {
        dfs1(it);
      } else if (ok[it] == 1) {
        flag = 1;
      }
    }
  }
  ok[nod] = 2;
}
int main() {
  int i, n, m;
  ios::sync_with_stdio(false);
  cin >> n >> m;
  for (i = 1; i <= m; i++) {
    cin >> x[i] >> y[i];
    g[x[i]].push_back(y[i]);
  }
  for (i = 1; i <= n && flag == 0; i++) {
    if (ok[i] == 0) {
      dfs(i);
    }
  }
  if (flag == 0) {
    cout << "YES";
    return 0;
  }
  int sz = edge.size();
  for (i = sz - 2; i >= 0; i--) {
    a = edge[i], b = edge[i + 1];
    if (i == sz - 2 || b != edge.back()) {
      memset(ok, 0, sizeof(ok));
      flag = 0;
      for (int j = 1; j <= n && flag == 0; j++) {
        if (ok[j] == 0) dfs1(j);
      }
      if (flag == 0) {
        cout << "YES";
        return 0;
      }
    } else
      break;
  }
  cout << "NO";
  return 0;
}
