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

namespace AtCoder20170211 {
	class Program {
		static void Main(string[] args) {
			var input = Console.ReadLine().Split(' ');

			var s = Convert.ToDecimal(input[0]);
			var c = Convert.ToDecimal(input[1]);

			var scc = 0m;

			if(s * 2 <= c) {
				scc = s;

				scc += Math.Floor((c - s * 2) / 4);
			}
			else {
				scc = Math.Floor(c / 2);
				//s -= scc;

				//scc += Math.Floor(s / 2);
			}
			Console.WriteLine(scc);
			//Console.ReadLine();
		}
	}
}