#!/bin/python3

import sys

def sumOfGroup(k):
    x = 1
    c = -1
    y = 0
    while x <= k :
        if x == k :
            c = (1+(y-1)*2)
            c += 2
            return ( ( k * (2*c + (k-1)*2) )//2 )
        else :
            y += x
        x += 1
    return 0    
    # Return the sum of the elements of the k'th group.

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