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;
using System.Text.RegularExpressions;
using System.Globalization;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            String[] str = Console.ReadLine().Split();
            long N = long.Parse(str[0]); /* Sの個数 */
            long M = long.Parse(str[1]); /* Cの個数 */
            long ans = 0;

            if (N < M/2)    /* Sが余る？ */
            {
                ans = N;
                M -= N * 2;
                ans += M / 4;
            }
            else            /* Sが足りない */
            {
                ans = M / 2;
            }

            Console.WriteLine(ans);
        }
    }
}