#include <bits/stdc++.h>
using namespace std;
int N, M;
const int MAX = 1e6;
vector<int> edges[MAX];
int indeg[MAX];
vector<int> source;
map<int, int> sink;
int reachable[20];
const int BITMAX = 1 << 20;
int dp[BITMAX];
void dfs(int start, int i) {
  if (sink.count(i)) {
    reachable[start] |= sink[i];
  } else {
    for (auto j : edges[i]) dfs(start, j);
  }
}
int main() {
  int i, j, k;
  cin >> N >> M;
  for (i = 0; i < M; i++) {
    int x, y;
    scanf("%d %d", &x, &y);
    edges[x - 1].push_back(y - 1);
    indeg[y - 1]++;
  }
  int num = 1;
  for (i = 0; i < N; i++) {
    if (indeg[i] == 0) source.push_back(i);
    if (edges[i].size() == 0) {
      sink[i] = num;
      num *= 2;
    }
  }
  int sz = source.size();
  for (i = 0; i < sz; i++) dfs(i, source[i]);
  int bitmax = 1 << sz;
  for (i = 1; i < bitmax; i++) {
    bool updated = false;
    int in = 0;
    for (j = 0; j < sz; j++) {
      if ((i >> j) & 1) {
        in++;
        if (!updated) {
          dp[i] = dp[i - (1 << j)] | reachable[j];
          updated = true;
        }
      }
    }
    int out = 0;
    for (j = 0; j < sz; j++) {
      if ((dp[i] >> j) & 1) out++;
    }
    if (in >= out && in < sz) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}
