func main()
	var n: int :: cui@inputInt()
	var k: int :: cui@inputInt()
	var ans: int :: 0
	if(k <> 1)
		if(n = k)
			do ans :: 1
		else
			do ans :: (n - k) * 2
		end if
	end if
	do cui@print("\{ans}\n")
end func