#include <bits/stdc++.h>
using namespace std;
const int maxn = 505;
int deg[maxn], ans[maxn], m, n;
vector<int> edge[maxn];
queue<int> que;
int topo() {
  int v, res = 0, crl[maxn];
  memset(crl, 0, sizeof(crl));
  for (int j = 1; j <= n; j++) {
    if (deg[j] == 0) {
      que.push(j);
    }
  }
  while (!que.empty()) {
    v = que.front();
    que.pop();
    ans[res++] = v;
    for (int j = 0; j < edge[v].size(); j++) {
      deg[edge[v][j]]--;
      crl[edge[v][j]]++;
      if (deg[edge[v][j]] == 0) que.push(edge[v][j]);
    }
  }
  for (int i = 1; i <= n; i++) {
    deg[i] += crl[i];
  }
  return res;
}
int main() {
  int tmp1, tmp2;
  scanf("%d%d", &n, &m);
  memset(deg, 0, sizeof(deg));
  for (int i = 1; i <= m; i++) {
    scanf("%d%d", &tmp1, &tmp2);
    edge[tmp1].push_back(tmp2);
    deg[tmp2]++;
  }
  for (int i = 0; i <= n; i++) {
    deg[i]--;
    tmp1 = topo();
    if (tmp1 == n) {
      puts("YES");
      return 0;
    }
    deg[i]++;
  }
  puts("NO");
  return 0;
}
