using System;

public class Classmiya
{
	static void Main()
	{
		string stdin = Console.ReadLine();
		string[] text = stdin.Split(' ');
		int A = int.Parse(text[0]);
		int B = int.Parse(text[1]);
		int count = 0;
		double average = 0.0;

		for (int i = A + 1; i < B; i++){
			average = (A + B + i) / 3.0;

			if(average == Convert.ToDouble(Convert.ToInt32(average))){
				count += 1;
			}
		}
		Console.WriteLine(count);
    }
}