View Code of Problem 4051

#include <bits/stdc++.h>
using namespace std;
int main(){

    int n;
    while(cin>>n){
            if(n<3){
        cout<<0<<endl;
    }
    else if(n%2==0){
        cout<<n/2 -1<<endl;
    }
    else{
        cout<<n/2<<endl;
    }
    }


    

    return 0;
}