#include <bits/stdc++.h>

using namespace std;

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int N, M;
    cin >> N >> M;
    vector<int> d(N);
    for (int i = 0; i < M; ++i)
    {
        int a, b;
        cin >> a >> b;
        d[b - 1]++;
        (void)a;
    }
    cout << ranges::count(d, 0) << endl;
}