#!/bin/python3

import sys

def sumOfGroup(k):
    before_kth_grp = (k-1)*k//2
    start = 2*before_kth_grp + 1
    end = start + 2*(k-1)
    return (start+end)//2*k

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