#include <bits/stdc++.h>
using namespace std;
long long INF = 1e18;
int INFi = 2e9;
double eps = 1e-6;
long long mod = 1e9 + 7;
vector<char> used;
vector<vector<int>> edge;
vector<int> p;
vector<int> cnt;
int sz = 0;
void add(int beg, int end) {
  while (beg != end) {
    cnt[beg]++;
    beg = p[beg];
  }
}
void sub(int beg) {
  while (used[beg] == 2) {
    cnt[beg]--;
    beg = p[beg];
  }
}
void dfs(int v) {
  used[v] = 1;
  for (int u : edge[v]) {
    if (used[u] == -1) {
      continue;
    }
    if (used[u] == 2) {
      sub(u);
      continue;
    }
    if (used[u] == 1) {
      add(v, u);
      sz++;
      continue;
    }
    p[u] = v;
    dfs(u);
  }
  used[v] = 2;
}
int main() {
  cin.tie(0);
  cout.tie(0);
  ios_base::sync_with_stdio(false);
  int n, m;
  cin >> n >> m;
  edge.resize(n);
  used.resize(n);
  p.resize(n);
  cnt.resize(n);
  int t1, t2;
  for (int i = 0; i < m; i++) {
    cin >> t1 >> t2;
    t1--;
    t2--;
    edge[t1].push_back(t2);
  }
  for (int i = 0; i < n; i++) {
    if (!used[i]) dfs(i);
    for (int j = 0; j < n; j++) {
      if (used[j] == 2) used[j] = -1;
    }
  }
  for (int i = 0; i < n; i++) {
    if (cnt[i] == sz) {
      cout << "YES\n";
      return 0;
    }
  }
  if (sz == 1) {
    cout << "YES\n";
  } else {
    cout << "NO\n";
  }
  return 0;
}
