#include <bits/stdc++.h>
using namespace std;
const int N = 505, M = 100005;
int n, m, k, u, v;
int head[N], in[N], rein[N];
struct edge {
  int v, next;
} e[M];
inline void add(int u, int v) {
  e[++k] = (edge){v, head[u]};
  head[u] = k;
  ++in[v];
}
inline bool TOPO(void) {
  register int cnt = 0;
  queue<int> q;
  for (register int i = 1; i <= n; ++i) {
    rein[i] = in[i];
    if (!in[i]) q.push(i);
  }
  while (!q.empty()) {
    register int u = q.front();
    q.pop();
    ++cnt;
    for (register int i = head[u]; i; i = e[i].next)
      if (--rein[e[i].v] == 0) q.push(e[i].v);
  }
  if (cnt == n) return true;
  return false;
}
int main(void) {
  scanf("%d%d", &n, &m);
  for (register int i = 1; i <= m; ++i) {
    scanf("%d%d", &u, &v);
    add(u, v);
  }
  for (register int i = 1; i <= n; ++i)
    if (in[i]) {
      --in[i];
      if (TOPO()) {
        puts("YES");
        return 0;
      }
      ++in[i];
    }
  puts("NO");
  return 0;
}
