#!/bin/python3

import sys

def sumOfGroup(k):
        n=k-1
        p=int(n*(n+1)/2)
        firstOddNumber=2*p+1
        totalSum=0
        
        for i in range (k):
            totalSum+=firstOddNumber
            firstOddNumber+=2
        
        return (totalSum)
    # Return the sum of the elements of the k'th group.

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