func main()
	var ss: [][]char :: cui@input().split(" ")
	var x: int :: ss[0].toInt(&)
	var y: int :: ss[1].toInt(&)
	
	if(math@gcd(x, y) <> 1)
		do cui@print("-1\n")
		ret
	end if
	
	var dp: []int :: #[x * y]int
	do dp[0] :: 1
	var ans: int :: 0
	for i(1, x * y - 1)
		var a: int :: i - x
		var b: int :: i - y
		if(a >= 0 & dp[a] = 1 | b >= 0 & dp[b] = 1)
			do dp[i] :: 1
			skip i
		end if
		do ans :+ 1
	end for
	do cui@print("\{ans}\n")
end func