#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    start = k * (k-1) + 1
    end = start + 2 * (k-1) + 1
    return sum( i for i in range(start,end,2))

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