using System;

namespace y
{
    class Program
    {
        static void Main(string[] args)
        {
            var ss = Console.ReadLine().Split();
            var x = int.Parse(ss[0]);
            var y = int.Parse(ss[1]);

            int ans = -1;
            if (x == y) ans = 0;
            else if (x == 0) ans = 2;
            else if (y == 0) ans = 1;
            Console.WriteLine(ans);
        }
    }
}