Given a set of numbers \textbf{\{1, 2, 3, 4, 5, … 2^n\}}. Alenka deletes from the set \textbf{2^\{(\}^\{n-1\}}^\{) \}numbers. Alex strikes out \textbf{2^\{(\}^\{n-2\}^\{)\}} numbers. Further strikes Alenka \textbf{2^\{(\}^\{n-3\}^\{)\}} numbers. And so on until there is some two numbers \textbf{a} and \textbf{b}. Then Alex gives Alenka |\textbf{a-b}| sweets. What is the maximum amount of candy can get Alena, Alex tends to lose if the candies as possible? \InputFile The input file contains one integer \textbf{n} (\textbf{n} < \textbf{1000}). \OutputFile Your program should output a single number - the maximum amount of candy that can win Alenka.