using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace Competitive.lib
{

    internal class Solution
    {
        public int A, B;

        public void Run()
        {
            var line = Input.ReadIntArray();
            A = line[0];
            B = line[1];

            int ret = 0;
            for (int i = A; i <= B; i++)
            {
                if ((A + B + i) % 3 == 0) ret++;
            }

            Console.WriteLine(ret);
        }
    }

    // libs ----------
    

    // common ----------

    internal static class Input
    {
        public static int ReadInt()
        {
            string line = Console.ReadLine();
            return int.Parse(line);
        }

        public static int[] ReadIntArray()
        {
            string line = Console.ReadLine();
            return line.Split(' ').Select(int.Parse).ToArray();            
        }

        public static double[] ReadDoubleArray()
        {
            string line = Console.ReadLine();
            return line.Split(' ').Select(double.Parse).ToArray();
        }
    }
    
    internal class Program
    {
        public static void Main(string[] args)
        {
            var s = new Solution();
            s.Run();
        }
    }
}