#!/bin/python3

import sys

def sumOfGroup(k):
    nSeenBefore = (k-1)*(k)//2;
    nSeenAtEnd = k*(k+1)//2;
    firstNum = nSeenBefore*2+1;
    lastNum = nSeenAtEnd*2-1;
    return (firstNum+lastNum)//2*k;

if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print( answer )