#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    h = 0
    for i in range (k+1):
        h = h+i

    s= [1]
    for i in range(1,h):
        s.append(s[i-1]+2)
    j = s[::-1]
    d = 0
    for i in range(k):
        d = d+j[i]
    return d

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