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.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] tmp = Console.ReadLine().Split(' ');
            double N = double.Parse(tmp[0]);
            double M = double.Parse(tmp[1]);

            // sに対しCが足りない
            if(M < 2*N)
            {
                if(M%2 == 0)
                {
                    Console.WriteLine(M / 2);
                }
                else
                {
                    Console.WriteLine((M - 1) / 2);
                }
            }
            else
            {
                // S に対しCがあまる
                double amari = M - 2 * N;
                double scc = N + Math.Floor(amari / 4);
                Console.WriteLine(scc);
            }

        }

    }
}