#!/bin/python3

import sys
def nextTerm(k):
    sum = 1
    for i in range(1,k):
        sum = sum + i
    return sum
def sumOfGroup(k):
    n = nextTerm(k)
    sum = 0
    for i in range(k):
        sum = (1 + (n-1) * 2) + sum
        n = n + 1
    return sum
    # Return the sum of the elements of the k'th group.

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