#!/bin/python3

import sys

def sumOdd(n):
    return (n + 1) * (n + 1)

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start = k * (k - 1) // 2
    end = start + k - 1
    return sumOdd(end) - sumOdd(start-1)
    

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