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: Runtime Error)

using System;
using System.Linq;

namespace abc_055_C
{
    class Program
    {
        public static int a = 0;
        static void Main(string[] args)
        {
            int[] gf = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int s = gf[0], c = gf[1];
            if (s * 2 < c)
            {
                while (s * 2 < c)
                {
                    c -= 2;
                    s++;
                }
                if (c % 2 == 1) { s--; }
                Console.WriteLine(s);

            }
            else
            {
                Console.WriteLine(s);
            }
            Console.ReadLine();   }
    }
}