C++ :

#include<cstdio>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
using namespace std;
int main()
{
    //freopen("A input.txt","r",stdin);
   // freopen("A output.txt","w",stdout);
    long long n;
    long long ans;
    while(cin>>n)
    {
        long long len=(n+1)/2;
        ans=(long long )((n-1)*(n-2)*n/6)-(long long )((n-len)*(n-len-1)*n/2);
        cout<<ans<<endl;

    }


    return 0;

}