func main()
	var a: int :: cui@inputInt()
	var b: int :: cui@inputInt()
	var ab: int :: a + b
	var c: int :: 1
	var ans: int :: -1
	while loop(true)
		if(c * c > ab)
			break loop
		end if
		if(ab % c = 0)
			var d: int :: ab / c
			if(f(a, b, c))
				if(ans = -1)
					do ans :: c
				else
					do ans :: [ans, c].min()
				end if
			end if
			if(f(a, b, d))
				if(ans = -1)
					do ans :: d
				else
					do ans :: [ans, d].min()
				end if
			end if
		end if
		do c :+ 1
	end while
	do cui@print("\{ans}\n")
	
	func f(a: int, b: int, c: int): bool
		if(a = c | b = c)
			ret false
		end if
		ret(c + a)%b = 0 & (b + c)%a = 0
	end func
end func