#include <bits/stdc++.h>
using namespace std;
const int maxn = 505;
const int maxm = 100;
const int inf = 2147483647;
const double eps = 1e-9;
const long long INF = 9223372036854775807ll;
long long qpow(long long a, long long b, long long c) {
  long long ans = 1;
  while (b) {
    if (b & 1) ans = ans * a % c;
    a = a * a % c;
    b >>= 1;
  }
  return ans;
}
vector<int> g[maxn];
int n;
int deg[maxn], dgg[maxn];
queue<int> q, f;
bool check(int k) {
  q = f;
  deg[k]--;
  if (!deg[k]) q.push(k);
  int cnt = 0;
  while (!q.empty()) {
    int u = q.front();
    q.pop();
    cnt++;
    for (register int i = (0); i < (g[u].size()); ++i) {
      int v = g[u][i];
      deg[v]--;
      if (!deg[v]) q.push(v);
    }
  }
  memcpy(deg, dgg, sizeof(int) * (n + 1));
  if (cnt == n) return true;
  return false;
}
int main() {
  int m;
  scanf("%d%d", &n, &m);
  for (register int i = (0); i < (m); ++i) {
    int u, v;
    scanf("%d%d", &u, &v);
    deg[v]++;
    g[u].push_back(v);
  }
  memcpy(dgg, deg, sizeof(int) * (n + 1));
  for (register int i = (1); i < (n + 1); ++i)
    if (!deg[i]) q.push(i);
  f = q;
  for (register int i = (1); i < (n + 1); ++i) {
    if (deg[i] && check(i)) return printf("YES\n"), 0;
  }
  printf("NO\n");
}
