#include<iostream>
using namespace std;

const int N = 100010;
int n, m;
bool st[N];

int main()
{
    scanf ("%d%d", &n, &m);

    int res = 0;
    for (int i = 0; i < m; i ++ ) 
    {
        int x, y;
        scanf ("%d%d", &x, &y);
        if (st[y] || y == 0) st[x] = true;
        else 
        {
            st[x] = true;
            res ++ ;
        }
    }

    cout << res << endl;

    return 0;
}