#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    return sum([2*n - 1 for n in range(k*(k-1)//2 + 1, k*(k-1)//2 + 1 + k)])

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