#include <bits/stdc++.h>
using namespace std;
const int MOD = 1e9 + 7;
const int qq = 500 + 10;
const int INF = 1e9 + 10;
vector<int> G[qq];
bool vis[qq];
int n, m, dag[qq], tmp[qq];
void dfs(int u) {
  vis[u] = true;
  for (int i = 0; i < G[u].size(); ++i) {
    int v = G[u][i];
    dag[v]--;
    if (!vis[v]) {
      if (dag[v] <= 0) {
        dfs(v);
      }
    }
  }
}
int main() {
  scanf("%d%d", &n, &m);
  for (int a, b, i = 0; i < m; ++i) {
    scanf("%d%d", &a, &b);
    G[a].push_back(b);
    tmp[b]++;
  }
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= n; ++j) {
      dag[j] = tmp[j];
    }
    dag[i]--;
    memset(vis, false, sizeof vis);
    for (int j = 1; j <= n; ++j) {
      if (!vis[j] && dag[j] <= 0) {
        dfs(j);
      }
    }
    bool ok = true;
    for (int j = 1; j <= n; ++j) {
      if (!vis[j]) {
        ok = false;
      }
    }
    if (ok) {
      printf("YES\n");
      return 0;
    }
  }
  printf("NO\n");
  return 0;
}
