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: Wrong Answer)

using System;
using System.Linq;
public class Aprob {
    public static void Main() {
        string[] readSome = new string[2];
        readSome = Console.ReadLine().Split(' ');
        long S = long.Parse(readSome[0]);
        long C = long.Parse(readSome[1]);
        long pairs = 0;
        if (S >= 2 * C) {
            pairs = S;
        } else {
            pairs = S;
            C -= 2 * S;
            S = 0;
            if (C % 2 == 1) {
                C--;
            }
            pairs += C / 4;
        }
        Console.WriteLine(pairs);
    }
}