#!/bin/python

import sys

def sumOfGroup(k):
    n = k - 1    
    start = (n*(n+1)) / 2
    current = 1 + start*2    
    total = 0
    for i in range(k):
        total += current
        current += 2
    return total
    

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