#include <bits/stdc++.h>
using namespace std;
vector<int> g[1000010];
int n, k;
bool r[1000010];
int s[1000010];
int m[1000010];
int main() {
  scanf("%d %d", &n, &k);
  for (int i = 0; i < k; i++) {
    int x, y;
    scanf("%d %d", &x, &y);
    g[x].push_back(y);
  }
  int v = 0;
  for (int i = 1; i <= n; i++) {
    if (r[i]) continue;
    s[v++] = i;
    r[i] = true;
    for (int j = 0; j < (int)g[i].size(); j++) r[g[i][j]] = true;
  }
  int sz = 0;
  for (int i = 1; i <= n; i++) r[i] = false;
  for (int i = v - 1; i >= 0; i--) {
    if (!r[s[i]]) {
      m[sz++] = s[i];
      for (int j = 0; j < (int)g[s[i]].size(); j++) r[g[s[i]][j]] = true;
    }
  }
  printf("%d\n", sz);
  for (int i = 0; i < sz; i++) printf("%d ", m[i]);
  printf("\n");
  return 0;
}
