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: Wrong Answer)

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

public class Remainder
{
    static public void Main ()
    {
        var NM = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToArray();
        var N = NM[0];
        var M = NM[1];
        var ans = 0L;
        
        if(M-2*N >= 0){
            ans = N+(M-2*N)/4;
        }
        
        
        
        Console.WriteLine(ans);

    }

}