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;

class MainClass {
  public static void Main (string[] args) {
    //入力
    var input = Console.ReadLine().Split(' ');
    var N = long.Parse(input[0]);
    var M = long.Parse(input[1]);
    var ans = (long)0;
    if(N * 2 <= M){
      ans = N;
      //作成作業
      ans += (M - N * 2) / 4;
    }else{
      ans = M / 2;
    }
    //出力
    Console.WriteLine(ans);
  }
}