http://cthbstalpha.blogspot.com/2016/05/ZJd881.html

ZJd881.cpp

#include<iostream>
using namespace std ;

int main(){
    int d ;

    while (cin >> d){
        int sum=0 ,ai=1 ,delta = 1 ;

        for (int i=1 ;i<=50 ;i++ ){
            sum += ai ;
            ai += delta ;
            delta += d ;
        }

        cout << sum <<endl ;
    }
}