#!/bin/python3

import sys

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

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