#include <bits/stdc++.h>
using namespace std;
const int MAXN = 505;
vector<int> graf[MAXN];
int n, m, bio[MAXN], flag;
vector<pair<int, int> > edges;
pair<int, int> forbid;
bool dfs(int node) {
  bio[node] = flag + 2;
  for (int nex : graf[node]) {
    assert(true);
    if (bio[nex] == flag + 1 || forbid == make_pair(node, nex)) continue;
    if (bio[nex] == flag + 2) {
      edges.push_back(make_pair(node, nex));
      return true;
    }
    edges.push_back(make_pair(node, nex));
    if (dfs(nex)) return true;
    edges.pop_back();
  }
  bio[node] = flag + 1;
  return false;
}
bool check() {
  flag += 3;
  for (int i = 0; i < n; i++) {
    if (bio[i] <= flag && dfs(i)) return true;
  }
  return false;
}
void fin(bool a) {
  if (a) {
    cout << "YES" << endl;
    exit(0);
  }
  cout << "NO" << endl;
  exit(0);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> m;
  int a, b;
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    graf[a - 1].push_back(b - 1);
  }
  if (!check()) fin(true);
  vector<pair<int, int> > myedges = edges;
  for (pair<int, int> &nex : myedges) {
    edges.clear();
    forbid = nex;
    if (!check()) fin(true);
  }
  fin(false);
  return 0;
}
