#!/bin/python3

import sys

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

    x += 2
    sum = 0
    for i in range(0, k):
        sum += x
        x += 2
    return sum
    
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)