#include <bits/stdc++.h>
using namespace std;
vector<vector<long long> > v;
void update_cyc(vector<long long>& cyc, vector<long long>& par, long long dest,
                long long sor) {
  while (dest != sor) {
    cyc.push_back(dest);
    dest = par[dest];
  }
  cyc.push_back(sor);
  reverse(cyc.begin(), cyc.end());
  return;
}
bool dfs(long long s, vector<long long>& vis, vector<long long>& par,
         vector<long long>& cyc, long long p) {
  vis[s] = 1;
  par[s] = p;
  bool val = false;
  for (long long i = 0; i < v[s].size(); i++) {
    long long u = v[s][i];
    if (!vis[u]) {
      val |= dfs(u, vis, par, cyc, s);
      if (val) return true;
    } else if (vis[u] == 1) {
      update_cyc(cyc, par, s, u);
      return true;
    }
  }
  vis[s] = 2;
  return val;
}
bool dfs1(long long s, vector<long long>& vis, long long a, long long b) {
  vis[s] = 1;
  bool val = false;
  for (long long i = 0; i < v[s].size(); i++) {
    long long u = v[s][i];
    if (s == a && b == u) continue;
    if (!vis[u]) {
      val |= dfs1(u, vis, a, b);
      if (val) return true;
    } else if (vis[u] == 1) {
      return true;
    }
  }
  vis[s] = 2;
  return val;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long n, m;
  cin >> n >> m;
  v.resize(n + 1);
  for (long long i = 0; i < m; i++) {
    long long a, b;
    cin >> a >> b;
    v[a].push_back(b);
  }
  vector<long long> cyc;
  vector<long long> vis(n + 1), par(n + 1);
  bool cnd = false;
  for (long long i = 1; i <= n; i++) {
    if (!vis[i]) {
      cnd |= dfs(i, vis, par, cyc, -1);
      if (cnd) break;
    }
  }
  if (!cnd) {
    cout << "YES" << endl;
    return 0;
  }
  long long k = cyc.size();
  for (long long i = 0; i < k; i++) {
    vis.clear();
    vis.resize(n + 1);
    bool val = false;
    for (long long j = 1; j <= n; j++) {
      if (!vis[j]) {
        val |= dfs1(j, vis, cyc[i], cyc[(i + 1) % k]);
      }
    }
    if (!val) {
      cout << "YES" << endl;
      return 0;
    }
  }
  cout << "NO" << endl;
  return 0;
}
