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

namespace algorithm
{
	class Program
	{
		public static void Main()
		{
			long[] nm = Array.ConvertAll(Console.ReadLine().Split(), long.Parse);
			long n = nm[0], m = nm[1]/2;
			
			long tmp = m-n;
			//M<N
			if (tmp < 0)
			{
				Console.WriteLine(m);
			}
			//N
			else if (tmp < 2)
			{
				Console.WriteLine(n);
			}
			//M>N
			else if (tmp > 1)
			{
				Console.WriteLine(n + tmp/2);
			}
			



		}
	}
}