#!/bin/python

import sys

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

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