#!/bin/python3

import sys


def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    n = k-1;
    ind = int(((n * (n+1)) / 2) + 1)

    start = ind*2-1
    sumog = 0
    for i in range (k):
        sumog += start+i*2
    
    return sumog
    
    

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