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: Accepted)

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

class Program
{
    static void Main(string[] args) {
#if DEBUG
        System.Diagnostics.Debug.WriteLine("-----TextFile1");
        System.Diagnostics.Debug.WriteLine(process("../TextFile1.txt"));
        System.Diagnostics.Debug.WriteLine("-----TextFile2");
        System.Diagnostics.Debug.WriteLine(process("../TextFile2.txt"));
        System.Diagnostics.Debug.WriteLine("-----TextFile3");
        System.Diagnostics.Debug.WriteLine(process("../TextFile3.txt"));
#endif

#if !DEBUG
        String ret = process(new System.IO.StreamReader(Console.OpenStandardInput()));
        Console.WriteLine(ret);
#endif
    }

    static string process(string filePath) {
        using (var input = new System.IO.StreamReader(filePath)) {
            if(input.EndOfStream) return "NO PROC";
            return process(input);
        }
    }

    static string process(System.IO.TextReader input) {
        var ss     = input.ReadLine();
        var spl   = ss.Split(' ');
        long s     = long.Parse(spl[0]);
        long c     = long.Parse(spl[1]);
        
        long r = 0;

        if(c <= s * 2) {
            r = c / 2;
        } else {
            r += s;
            c -= s * 2;
            r += c / 4;
        }
        return r + "";
    }
    
}