#include <bits/stdc++.h>
int n, m;
int g[505][505] = {0};
int vis[505] = {0};
int ring[505] = {0};
int nring = 0;
int chk[505] = {0};
int checkring(int cur) {
  if (chk[cur] == -1) return 0;
  chk[cur] = -1;
  for (int next = 1; next <= n; ++next) {
    if (chk[next] != 1 && g[cur][next] == 1) {
      if (0 == checkring(next)) {
        return 0;
      }
    }
  }
  chk[cur] = 1;
  return 1;
}
int findring(int cur, int rdx) {
  if (vis[cur] == -1) {
    ring[rdx] = cur;
    nring = rdx;
    return 1;
  }
  vis[cur] = -1;
  for (int next = 1; next <= n; ++next) {
    if (vis[next] != 1 && g[cur][next] == 1) {
      if (1 == findring(next, rdx + 1)) {
        ring[rdx] = cur;
        return 1;
      }
    }
  }
  vis[cur] = 1;
  return -1;
}
int main() {
  scanf("%d %d", &n, &m);
  int a1, a2;
  for (int i = 0; i < m; ++i) {
    scanf("%d %d", &a1, &a2);
    g[a1][a2] = 1;
  }
  for (int i = 1; i <= n; ++i) {
    nring = 0;
    if (1 == findring(i, 0)) {
      break;
    }
  }
  int pflag = 0, rflag;
  if (nring == 0) {
    printf("YES");
    return 0;
  }
  ++nring;
  for (int i = 0; i < nring && pflag == 0; ++i) {
    memset(chk, 0, sizeof chk);
    g[ring[i]][ring[(i + 1) % nring]] = 0;
    rflag = 1;
    for (int t = 1; t <= n && rflag; ++t) rflag = checkring(t);
    pflag = rflag;
    g[ring[i]][ring[(i + 1) % nring]] = 1;
  }
  if (pflag)
    printf("YES");
  else
    printf("NO");
}
