#include <bits/stdc++.h>
using namespace std;
int n, k, a[100005];
int main() {
scanf("%d%d", &n, &k);
int res = 0;
for (int i = 1; i <= k; i ++ ) {
int x, y;
scanf("%d%d", &x, &y);
if (y != 0 && a[y] == 0) res++;
a[x] = 1;
}
printf("%d\n", res);
return 0;
}