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

namespace AtCoderBeginnerContest055
{
    class ProgramC

    {
        static void Main(string[] args)
        {
            string szLine = Console.ReadLine();
            string[] szArr = szLine.Split(' ');
            long n = int.Parse(szArr[0]);
            long m = int.Parse(szArr[1]);

            long max = 0;
            if (2 * n >= m)
            {
                max = m / 2;
            }
            else
            {
                // 2c 個から c個のsを作る
                long c = (long)((double)(m - 2 * n) / 4);
                max = n + c;
            }
            Console.WriteLine(max);
        }
    }
}