#include <bits/stdc++.h>
using namespace std;
void fast() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
}
vector<vector<int> > adj(1e4);
vector<int> vis(1e4, 0);
vector<pair<int, int> > s;
int POP = 0, y = -1, Done = 0;
int Mark = 1;
int n, m;
void initialize() {
  fill(vis.begin(), vis.end(), 0);
  Mark = 1;
}
void check(int u) {
  vis[u] = 1;
  for (auto x : adj[u]) {
    if (x == -1) continue;
    if (vis[x] == 1) Mark = 0;
    if (!vis[x]) {
      check(x);
    }
  }
  vis[u] = 2;
}
void dfs(int u) {
  vis[u] = 1;
  if (Done) return;
  for (auto x : adj[u]) {
    if (!vis[x]) dfs(x);
    if (vis[x] == 1) {
      POP = 1;
      y = x;
    }
    if (POP && (!Done)) {
      s.push_back(make_pair(u, x));
      if (u == y) {
        Done = 1;
        break;
      }
      break;
    }
  }
  vis[u] = 2;
}
int main() {
  cin >> n >> m;
  for (long long i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    adj[x].push_back(y);
  }
  for (long long i = 1; i < n + 1; i++) {
    if (Done) break;
    if (!vis[i]) dfs(i);
  }
  if (s.empty()) {
    cout << "YES";
    return 0;
  }
  for (auto k : s) {
    int x = k.first, y = k.second;
    auto p = adj[x].begin();
    while (p != adj[x].end()) {
      if ((*p) == y) {
        (*p) = -1;
      }
      p++;
    }
    initialize();
    for (long long i = 1; i < n + 1; i++) {
      if (!vis[i]) check(i);
    }
    if (Mark) {
      cout << "YES";
      return 0;
    }
    p = adj[x].begin();
    while (p != adj[x].end()) {
      if ((*p) == -1) {
        (*p) = y;
      }
      p++;
    }
  }
  cout << "NO";
}
