#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    i = (k*(k-1))//2
    o1 = 1 + 2*i
    o2 = o1 + 2*(k-1)
    sum = (k*(o1+o2))//2
    return int(sum)

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