#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    total = k * (k+1) / 2
    start_pos = int(total - (k - 1))
    start_odd = start_pos * 2  - 1
    sum = 0
    for i in range(k):
        #print(start_odd + 2*i)
        sum += start_odd + 2*i
    return sum

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