using System;

namespace No._682
{
    class Program
    {
        static void Main(string[] args)
        {
            var arr = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
            int a = arr[0];
            int b = arr[1];

            //double avg = 0;
            var len = arr.Length;
            int count = 0;
            for (var i = a; i <= b; i++)
            {
                if (int.TryParse(((double)(a + b + i) / 3).ToString(), out int avg)) count++;                                        
            }
            Console.WriteLine(count);
        }
    }
}