Problem:
Score : 300 points

Problem Statement

Snuke loves puzzles.

Today, he is working on a puzzle using S- and c-shaped pieces.
In this puzzle, you can combine two c-shaped pieces into one S-shaped piece, as shown in the figure below:

Snuke decided to create as many Scc groups as possible by putting together one S-shaped piece and two c-shaped pieces.

Find the maximum number of Scc groups that can be created when Snuke has N S-shaped pieces and M c-shaped pieces.

Constraints

1 ≤ N,M ≤ 10^{12}

Input

The input is given from Standard Input in the following format:

N M

Output

Print the answer.

Sample Input 1

1 6

Sample Output 1

2

Two Scc groups can be created as follows:

Combine two c-shaped pieces into one S-shaped piece

Create two Scc groups, each from one S-shaped piece and two c-shaped pieces

Sample Input 2

12345 678901

Sample Output 2

175897

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCoderRegularContest069
{
    public class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(program1(new String[] { Console.ReadLine() }));
            Console.ReadLine();
        }

        public static string program1(string[] args)
        {
            var n = int.Parse(args[0]);
            var s = args[1].ToCharArray();

            var animalPattern = new List<char>[] { new List<char>() { 'c', 'c' }, new List<char> { 'c', 'w' }, new List<char> { 'w', 'w' }, new List<char> { 'w', 'c' } };

            return string.Join("", animalPattern.Select(animals =>
            {
                var prevAnimal = animals.First();
                             
                foreach(var ans in s.Skip(1))
                {
                    var last = animals.Last();

                    if (last == 'c')
                    {
                        if (ans == 'x')
                        {
                            animals.Add(prevAnimal == 'c' ? 'w' : 'c');
                        }
                        else animals.Add(prevAnimal);
                    }
                    else
                    {
                        if (ans == 'o')
                        {
                            animals.Add(prevAnimal == 'c' ? 'w' : 'c');
                        }
                        else animals.Add(prevAnimal);
                    }
                    prevAnimal = last;
                }

                return animals;
            }).FirstOrDefault(animals => {
                if (animals.First() == animals.Last())
                {
                    if (s.First() == 'o')
                    {
                        return animals.ElementAt(1) == animals.ElementAt(n - 1);
                    }
                    else
                    {
                        return animals.ElementAt(1) != animals.ElementAt(n - 1);
                    }
                }
                else return false;
            })?.Take(n) ?? new List<char>() { '-', '1' }) ;
        }
    }
}