#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    res = k * (k+1)//2
    ans = 0
    start = res *2 +1 
    #print(ans, start, res)
    for i in range(k+1):
        ans += start
        start +=2
    return ans

if __name__ == "__main__":
    k = int(input().strip())
    answer = sumOfGroup(k-1)
    print(answer)