// P2419 牛大赛。胜者指向败者，闭包后判断是否与其余点全部可比较。
#include <bits/stdc++.h>
using namespace std;
int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    int n, m; if (!(cin >> n >> m)) return 0;
    vector<vector<bool>> reach(n, vector<bool>(n, false));
    for (int i = 0, a, b; i < m; ++i) { cin >> a >> b; reach[a-1][b-1] = true; }
    for (int k = 0; k < n; ++k) for (int i = 0; i < n; ++i) for (int j = 0; j < n; ++j)
        reach[i][j] = reach[i][j] || (reach[i][k] && reach[k][j]);
    int ans = 0;
    for (int v = 0; v < n; ++v) {
        int known = 0;
        for (int j = 0; j < n; ++j) {
            if (j == v) continue;
            if (reach[v][j] || reach[j][v]) ++known;
        }
        if (known == n-1) ++ans;
    }
    cout << ans << '\n';
}