using System;
//using System.Collections.Generic;
using System.Linq;
//using System.Text;

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var va = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int na = (va[0] + va[1] + va[0] + 2) / 3;
            int nb = (va[0] + va[1] + va[1]) / 3;

            Console.WriteLine(nb - na + 1);
            //Console.ReadLine();
        }
    }
}