#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    long long N, M, A, B;
    scanf("%ld %ld", &N, &M);
    long long *deg = (long long *)calloc(N, sizeof(long long));
    for (long long i = 0; i < M; ++i)
    {
        scanf("%ld %ld", &A, &B);
        deg[B - 1]++;
    }
    long long ans = 0;
    for (int i = 0; i < N; ++i)
    {
        if (deg[i] == 0)
            ans++;
    }
    printf("%ld\n", ans);
    free(deg);
    return 0;
}