#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    nthelement = ((k-1)*k/2)+1
    odd = 2*nthelement - 1
    sum= 0 
    while(k):
        sum = sum + odd
        odd += 2
        k -= 1
    return sum

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