func main()
	var x: int :: cui@inputInt()
	var ans: int :: -1
	for n([x - 100, 1].max(), x + 100)
		if((n $ bit64).xor(hammingWeight(n)) = x $ bit64)
			do ans :: n
			break n
		end if
	end for
	do cui@print("\{ans}\n")
	
	func hammingWeight(n: int): bit64
		var res: int :: 0
		while(n <> 0)
			if(n % 2 = 1)
				do res :+ 1
			end if
			do n :/ 2
		end while
		ret res $ bit64
	end func
end func