#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    sum_prev = ((k-1)*k)/2
    first = (2*sum_prev) + 1
    sum_group = sum(range(first, 2*(k-1)+first+2,2))
    return sum_group

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