#!/bin/python

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    s=1
    p=1
    i=1
    q=1
    while i<k:
        s+=p
        q+=1
        p=q
        i+=1
    j=2*s-1
    i=0
    su=0
    while i<k:
        su+=j
        j=j+2
        i+=1
    return su

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