#include <bits/stdc++.h>
using namespace std;
int i, n, m, ans, x, l, r, tot, a[1000005], b[1000005], last[1000005],
    to[1000005], Next[1000005], q[1000005], y;
inline void add(int x, int y) {
  Next[++tot] = last[x];
  last[x] = tot;
  to[tot] = y;
}
inline bool check(int x) {
  for (int i = 1; i <= n; i++) a[i] = b[i];
  a[x]--;
  int rr = r, ll = l;
  q[++r] = x;
  while (l < r) {
    int k = q[++l];
    for (int i = last[k]; i; i = Next[i]) {
      a[to[i]]--;
      if (!a[to[i]]) q[++r] = to[i];
    }
  }
  if (r == n) return true;
  r = rr, l = ll;
  return false;
}
int main() {
  scanf("%d%d", &n, &m);
  for (i = 1; i <= m; i++) scanf("%d%d", &x, &y), b[y]++, add(x, y);
  for (i = 1; i <= n; i++)
    if (b[i] == 0) q[++r] = i;
  while (l < r) {
    int k = q[++l];
    for (int i = last[k]; i; i = Next[i]) {
      b[to[i]]--;
      if (!b[to[i]]) q[++r] = to[i];
    }
  }
  if (r == n) return puts("YES"), 0;
  for (i = 1; i <= n; i++) {
    if (b[i] == 1) {
      if (check(i)) return puts("YES"), 0;
    }
  }
  puts("NO");
}
