I think that all correct or mistake on variable???
//#1502
#include<iostream.h>

int main()
{
long long s=0;
long k,i,n;
cin>>n;

for(i=0;i<=n;i++)
s+=(i + n) * (n - i + 1) / 2 + i * (n - i + 1);
cout<<s;
return 0;
}

Edited by author 25.11.2006 08:14

Compilation Error!

#include <iostream>
using namespace std;
...

Thank you.
спасибо Антон.