View Code of Problem 4051

#include <iostream>

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;
    }
}