#include <iostream>
#include <cstring>
#include <vector>
using namespace std;
const int N = 1010;
vector<int> v[N], w[N];
int n, m;
int visited[N], vis2[N];

void dfs1(int x) {
    visited[x] = 1;
    for (int i = 0; i < v[x].size(); i++) {
        if (!visited[v[x][i]]) {
            dfs1(v[x][i]);
        }
    }
    return ;
}

void dfs2(int x) {
    vis2[x] = 1;
    for (int i = 0; i < w[x].size(); i++) {
        if (!vis2[w[x][i]]) {
            dfs2(w[x][i]);
        }
    }
    return ;
}

int main() {
    int res = 0;
    cin >> n >> m;


    for (int i = 1; i <= m; i++) {
        int a, b;
        cin >> a >> b;
        v[a].push_back(b);
        w[b].push_back(a);
    }
    for (int i = 1; i <= n; i++) {
        int f = 1;
        memset(visited, 0, sizeof visited);
        memset(vis2, 0, sizeof vis2);
        dfs1(i);
        dfs2(i);
        for (int i = 1; i <= n; i++) {
            if (!visited[i] && !vis2[i]) {
                f = 0;
                break;
            }
        }
        if (f)
            res++;
    }
    cout << res << endl;

    return 0;
}