#include <bits/stdc++.h>
#pragma GCC target("sse,sse2,sse3,sse3,sse4,popcnt,abm,mmx")
using namespace std;
const int mod = 1e9 + 7;
const int N = 5e2 + 5;
vector<int> g[N];
int cl[N];
int b1 = -1, b2 = -1;
int p[N];
int st = -1, en = -1;
int a[N][N];
bool dfs(int v, int pr) {
  cl[v] = 1;
  for (int i = 0; i < g[v].size(); ++i) {
    int to = g[v][i];
    if (v == b1 && to == b2) continue;
    if (cl[to] == 0) {
      p[to] = v;
      if (dfs(to, v)) return true;
    } else if (cl[to] == 1) {
      st = to;
      en = v;
      return true;
    }
  }
  cl[v] = 2;
  return false;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  srand(time(0));
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x >> y;
    x--;
    y--;
    g[x].push_back(y);
    a[x][y]++;
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
    }
  }
  for (int i = 0; i < n; i++) p[i] = -1;
  st = -1, en = -1;
  for (int i = 0; i < n; i++) {
    if (cl[i]) continue;
    dfs(i, -1);
    if (st != -1) break;
  }
  if (st == -1) {
    cout << "YES";
    return 0;
  }
  set<int> on;
  int it = 0;
  while (st != en && it < n) {
    on.insert(en);
    en = p[en];
    it++;
  }
  on.insert(st);
  vector<pair<int, int> > e;
  for (auto v : on) {
    for (auto x : g[v]) {
      if (on.count(x)) {
        e.push_back({v, x});
      }
    }
  }
  for (auto x : e) {
    b1 = x.first, b2 = x.second;
    for (int i = 0; i < n; i++) cl[i] = 0;
    st = -1;
    en = -1;
    for (int i = 0; i < n; i++) {
      if (cl[i]) continue;
      dfs(i, -1);
      if (st != -1) break;
    }
    if (st == -1) {
      cout << "YES";
      return 0;
    }
  }
  cout << "NO";
  return 0;
}
