#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.

    startI = (k - 1) * k / 2 + 1
    startNum = (startI * 2  - 1)
    endI = k * (k + 1) / 2
    endNum = (endI * 2 - 1)
    
    total = 0
    for i in xrange(startNum, endNum + 1, 2):
        total += i
    return total

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