Candy

Given a set of numbers {1, 2, 3, 4, 5, … 2^n}. Alenka deletes from the set 2^{(}^{n-1}^{) }numbers. Alex strikes out 2^{(}^{n-2}^{)} numbers. Further strikes Alenka 2^{(}^{n-3}^{)} numbers. And so on until there is some two numbers a and b. Then Alex gives Alenka |a-b| sweets. What is the maximum amount of candy can get Alena, Alex tends to lose if the candies as possible?

Input

The input file contains one integer n (n < 1000).

Output

Your program should output a single number - the maximum amount of candy that can win Alenka.

Examples