#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    num_prev_elements = 0
    sum_k_elements = 0
    for i in range(1,k):
        num_prev_elements += i
    for j in range(1,k+1):
        sum_k_elements = sum_k_elements + (((num_prev_elements + j)*2) - 1)
    return sum_k_elements
        
if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k)
    print(answer)