using System.Numerics;

public class Program
{
    public static void Main()
    {
        
        //int num = int.Parse(Console.ReadLine() ?? string.Empty);
        string[] str = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');
        //string str = Console.ReadLine() ?? string.Empty;

        int a = int.Parse(str[0]);
        int b = int.Parse(str[1]);

        int count = 0;
        for(int i = a; i <= b; i++)
        {
            double d = ((double)a + (double)b + (double)i) / 3;
            if(d.ToString().IndexOf('.') ==-1)
            {
                count++;
            }
        }
        Console.WriteLine(count);

    }
}