#include<iostream>
using namespace std;

int main() {
    int n,k;
    cin>>n>>k;
    bool*initialize=new bool[n]{false};
    int result=0,x,y;
    while(k--){
        cin>>x>>y;
        if(y&&!initialize[y-1]){
            result++;
        }
        initialize[x-1]= true;
    }
    cout<<result;
}