#include <bits/stdc++.h>
int dx[] = {-1, -1, -1, 0, 1, 1, 1, 0};
int dy[] = {-1, 0, 1, 1, 1, 0, -1, -1};
using namespace std;
long long power(long long a, long long p, long long M) {
  long long r = 1;
  a = a % M;
  while (p > 0) {
    if (p % 2) r = (r * a) % M;
    a = (a * a) % M;
    p /= 2;
  }
  return r;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long n, m;
set<long long> e[100005];
stack<long long> cycle, temp;
long long vis[505];
bool found;
void findCycle(long long x) {
  temp.push(x);
  vis[x] = 1;
  for (auto y : e[x]) {
    if (vis[y] == 0)
      findCycle(y);
    else if (vis[y] == 1) {
      if (found) return;
      cycle = temp;
      cycle.push(y);
      found = 1;
      return;
    }
  }
  if (!temp.empty()) temp.pop();
  vis[x] = 2;
}
void fc(long long x) {
  vis[x] = 1;
  for (auto y : e[x]) {
    if (vis[y] == 0)
      fc(y);
    else if (vis[y] == 1) {
      found = 1;
      return;
    }
  }
  vis[x] = 2;
}
void solve() {
  cin >> n >> m;
  for (long long i = 0; i < m; i++) {
    long long a, b;
    scanf("%lld%lld", &a, &b);
    e[a].insert(b);
  }
  for (long long i = 1; i < n + 1; i++) {
    if (!vis[i]) {
      findCycle(i);
      if (found) break;
    }
  }
  if (!found) {
    cout << "YES\n";
    return;
  }
  vector<long long> c;
  for (long long i = 0; i < 505; i++) vis[i] = 0;
  while (!cycle.empty()) {
    c.push_back(cycle.top());
    if (vis[cycle.top()]) {
      break;
    }
    vis[cycle.top()] = 1;
    cycle.pop();
  }
  reverse(c.begin(), c.end());
  for (long long i = 0; i < c.size() - 1; i++) {
    found = 0;
    e[c[i]].erase(c[i + 1]);
    for (long long j = 0; j < 505; j++) vis[j] = 0;
    for (long long j = 1; j < n + 1; j++) {
      if (!vis[j]) fc(j);
      if (found) {
        break;
      }
    }
    if (!found) {
      cout << "YES\n";
      return;
    }
    e[c[i]].insert(c[i + 1]);
  }
  cout << "NO\n";
}
int main() {
  solve();
  return 0;
}
