#include<iostream>

#include<cstdio>

using namespace std;

int main(){

 freopen("2015coin.in","r",stdin);

 freopen("2015coin.out","w",stdout);

 int n,t=0;

 cin>>n;

 for(int i=1;;i++){

 if(n-i>0){

 n=n-i;

 t+=i*i;

 }

 else{

 t+=i*n;

 break;

 }

 }

 cout<<t;

 return 0;

}