#include <iostream>
using namespace std;

int edge[2010][2010];
int tmp[2020];
int arr[2020];

void merge_sort(int idx, int _n) {
    if (_n == 1) return;
    auto t = _n / 2;
    merge_sort(idx, t);
    merge_sort(idx + t, _n - t);
    int i = idx, j = idx + t;
    int cnt = 0;
    while (i < idx + t && j < idx + _n) {
        if (edge[arr[i]][arr[j]]) {
            tmp[cnt++] = arr[i++];
        }
        else {
            tmp[cnt++] = arr[j++];
        }
    }
    while (i < idx + t) {
        tmp[cnt++] = arr[i++];
    }
    while (j < idx + _n) {
        tmp[cnt++] = arr[j++];
    }
    for (int k = 0; k < _n; k++) {
        arr[idx + k] = tmp[k];
    }
    return;
}

int main(){
    int n, m;
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        edge[a - 1][b - 1] = 1;
    }
    for (int i = 0; i < n; i++) arr[i] = i;
    merge_sort(0, n);
    cout << n - 1 << endl;
    for (int i = 0; i < n; i++) cout << arr[i] + 1 << (i == n - 1? "\n": " ");
    return 0;
}