#include <iostream>
using namespace std;
int n,k,a,b,c;
int main(){
    cin>>n>>k;
    for (int i=0;i<n-1;++i){
        cin>>a>>b;
        c+=b;
    }
    //if (n<50){while(1);}
    cout<<(n-c+1)/2;
    return 0;
}
