#!/bin/python3

import sys

def sumOfGroup(k):
    # Return the sum of the elements of the k'th group.
    #print((k*(k-1)+1))
    start = (k*(k-1)+1)
    #print("Start = ",start)
    diff = (k-1)*2
    #print("Diff =",diff)
    end = start + diff
    #print("End =",end)
    endElementNum = int((end+1)/2)
    #print("EndElementNum ",endElementNum)
    startElementNum = int((start+1)/2)
    #print("StartElementNum ",startElementNum)
    prevSetOdd = startElementNum-1
    #print("start^2=",prevSetOdd*prevSetOdd)
    #print("end^2=",endElementNum*endElementNum)
    startSquare = prevSetOdd*prevSetOdd
    endSquare = endElementNum*endElementNum    
    return endSquare-startSquare

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