using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;

class Program
{
    static void Main()
    {
        var AB = ReadLine().Split().Select(int.Parse).ToArray();
        var a = 0;
        for (int i = AB[0]; i <= AB[1]; i++)
        {
            if ((AB.Sum() + i) % 3 == 0) a++;
        }
        WriteLine(a);
    }
}