#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    result = 0
    f = int((1 + (k-1)*k/2) * 2 - 1)
    for n in range(0, k * 2, 2):
        result += f + n
    return result

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