#include <iostream>
#include <vector>

using namespace std;

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

    int N, M, A, B, i, ans = 0;
    cin >> N >> M;
    vector<int> count(N, 0);

    for (i = 0; i != M; ++i)
        cin >> A >> B, ++count[B - 1];

    for (i = 0; i != N; ++i)
        if (count[i] == 0)
            ++ans;

    cout << ans << '\n';
    return 0;
}