#include <iostream>
using namespace std;
int main(){
    int n;  cin >> n;
    int sum = 0;
    int cnt = 1;
    while(n >= cnt && n){
        sum += cnt * cnt;
        n -= cnt;
        cnt ++ ;
    }
    if(n)   sum += cnt * n;
    cout << sum << endl;
    return 0;
}