import Data.Text as T
pow_ n 1 = n
pow_ n m = n*pow_ n (m-1)
check m 1 = (pow_ 2 (m-1))-m
check m n 
	| m > n = pow_ 2 (m-n)
	| m == n = 1
	| otherwise = 0
main = do
	str<-getLine
	let data_=T.split (==' ') (T.pack str)
	let v1 = read$unpack$data_!!0::Int
	let v2 = read$unpack$data_!!1::Int
	putStrLn$show$check v1 v2