#!/bin/python3

import sys

def sumOfGroup(k):
    k1=k-1
    k1=(k1*(k1+1))//2
    k1=1+2*(k1-1)
    k1+=2
    l=0
    while(k):
        l+=k1
        k1+=2
        k-=1
    return(l)
    # Return the sum of the elements of the k'th group.

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