#!/bin/python3

import sys

def sumOfGroup(k):
    low=sum(range(k))
    high=low+k
    h=high*2-1
    l=low*2-1
    return sum([i for i in range(h, l, -2)])
        

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