#include <bits/stdc++.h>
using namespace std;
int n, m, kol, cnt, all;
vector<int> qqq;
int used2[505];
int pred[505];
bool used[505];
vector<int> v[505];
vector<int> vv[505];
int clr[505];
vector<int> qq;
vector<int> q;
bool dfs3(int x, int y) {
  used2[x] = 1;
  pred[x] = y;
  for (int i = 0; i < v[x].size(); ++i) {
    int to = v[x][i];
    if (used2[to] == 2) continue;
    if (used2[to] == 0) {
      if (dfs3(to, x)) return true;
      continue;
    }
    while (x != to) {
      qqq.push_back(x);
      x = pred[x];
    }
    qqq.push_back(to);
    return true;
  }
  used2[x] = 2;
  return false;
}
bool dfs4(int x, int y, int xx, int yy) {
  used2[x] = 1;
  for (int i = 0; i < v[x].size(); ++i) {
    int to = v[x][i];
    if (x == xx && to == yy) continue;
    if (used2[to] == 2) continue;
    if (used2[to] == 0) {
      if (dfs4(to, x, xx, yy)) return true;
      continue;
    }
    return true;
  }
  used2[x] = 2;
  return false;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m;
  for (int i = 1; i <= m; ++i) {
    int x, y;
    cin >> x >> y;
    v[x].push_back(y);
    vv[y].push_back(x);
  }
  for (int i = 1; i <= n; ++i)
    if (dfs3(i, -1)) break;
  if (qqq.size() == 0) {
    cout << "YES";
    return 0;
  }
  reverse(qqq.begin(), qqq.end());
  for (int i = 0; i < qqq.size(); ++i) {
    int x = qqq[i];
    int y;
    if (i < qqq.size() - 1)
      y = qqq[i + 1];
    else
      y = qqq[0];
    memset(used2, 0, sizeof(used2));
    bool t = false;
    for (int i = 1; i <= n; ++i)
      if (dfs4(i, -1, x, y)) {
        t = true;
        break;
      }
    if (t == false) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
}
