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

class Class_
{
	void Test()
	{
		var NM = A_Long_();
		var N = NM[0];
		var M = NM[1];

		if (N>M*2) {
			Console.WriteLine(N);
		} else {
			var a = N;
			var b = (M-2*N)/ 4;
			Console.WriteLine(a+b);
		}
		


	}

	static void Main(string[] args)
  {
    new Class_().Test();
  }

  #region

  string S_String_()
  {
    return Console.ReadLine();
  }

	//
	string[] A_String_()
  {
    return Console.ReadLine().Split();
  }

  int[] A_Int_(int n)
  {
    var x = new int[n];
    for (var i = 0; i < n; i++)
    {
      x[i] = int.Parse(Console.ReadLine());
    }
    return x;
  }

	//
	int[] A_Int_()
  {
    var ss = Console.ReadLine().Split();

    var x = new int[ss.Length];
    for (var i = 0; i < ss.Length; i++)
      x[i] = int.Parse(ss[i]);

    return x;
  }

	long[] A_Long_()
	{
		var ss = Console.ReadLine().Split();

		var x = new long[ss.Length];
		for (var i = 0; i < ss.Length; i++)
			x[i] = long.Parse(ss[i]);

		return x;
	}

	#endregion
}