#!/bin/python

import sys

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

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