#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    x = 0
    for i in range(1, k):
        x += i
    x = x * 2 + 1
    lst = []
    lst.append(x)
    for j in range(k-1):
        x += 2
        lst.append(x)

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