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# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.IO.Compression;
using System.Linq;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Text;
using System.Text.RegularExpressions;
using Console = System.Console;

namespace Atcoder
{

    class Program
    {
        private const long COMDIV = 1000000007;

        static void Main(string[] args)
        {
            var NM = Console.ReadLine().Split().Select(long.Parse).ToArray();
            if (NM[0] * 2 >= NM[1])
            {
                Console.WriteLine(Math.Truncate((double)NM[1] / 2));
            }
            else
            {
                var remain = NM[1] - NM[0] * 2;
                Console.WriteLine(NM[0] + Math.Truncate((double)remain / 4));
            }
        }
    }
}