using System.IO;

namespace ttt
{
    internal class Program
    {
        static void Main(string[] args)
        {
            string inp = Console.ReadLine();
            int[] nums = inp.Split(' ').Select(int.Parse).ToArray();
            int a = nums[0], b = nums[1], count = 0;
            
            for (int c = a; c <= b; c++)
                if ((a + b + c) % 3 == 0)
                    count++;

            Console.WriteLine(count);
        }
    }
}