#!/bin/python

import sys

def sumOfGroup(k):
    sum=0
    t=k*(k-1)+1
    while (k>0) :
        sum+=t
        t+=2
        k=k-1
    # Return the sum of the elements of the k'th group.
    return sum

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