#include <iostream>
using namespace std;

int main() {
    int a;
    cin >>a;
    int j =0;
    int i = 0;
    int sum = 0;
    while(i<=a)
    {
        while(j<=i)
        {
            sum = j+sum;
            j++;
        
        }
        j = 0;
        i++;
    }
    cout <<sum;

    
}
// 64 位输出请用 printf("%lld")