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;

namespace ABC055_C_Scc_Puzzle
{
	internal class Program
	{
		public static void Main(string[] args)
		{
			string[] input = Console.ReadLine().Split(' ');
			long n = long.Parse(input[0]);
			long m = long.Parse(input[1]);

			long count;
			if (n <= m / 2)
			{
				//sのパーツを全て使い切る
				count = n;
				m -= n * 2;
				//残りのmでできる限り作る(c4つで1セット)
				count += m / 4;
			}
			else
			{
				count = m / 2;
			}
			
			Console.WriteLine(count);
		}
	}
}