#include <fstream>
#include <vector>

using namespace std;

#define NMAX 100000
#define MMAX 200000

vector<int> v[NMAX];
int f[NMAX + 1], ans[NMAX + 1];
int vx[MMAX + 1];

void DFS( int node ) {
    for ( auto copil : v[node] ) {
        f[copil]++;
        if ( f[copil] == 1 ) {
            ans[copil] = 1;
            DFS(copil);
        }
        f[copil]--;
    }
}

ifstream cin ("dfs.in");
ofstream cout ("dfs.out");

int main() {
    int n, m, i, x, y, cnt;
    cin >> n >> m;
    for ( i = 0; i < m; i++ ) {
        cin >> x >> y;
        vx[i] = x;
        v[x].push_back(y);
    }
    for ( i = 0; i < m; i++ ) {
        DFS(vx[i]);
    }
    cnt = 0;
    for ( i = 0; i < n; i++ ) {
        cnt += ans[i];
    }
    cout << cnt << "\n";
    return 0;
}