#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    n = k-1
    st_index = int((n*(n+1))/2 + 1)
    end_index = int((k*(k+1))/2 + 1)
    return sum(range(st_index*2-1, end_index*2-1, 2))

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