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.Numerics;
class neet{
  public static void Main(String[] args){
    var a =Console.ReadLine();
    String [] b = a.Split();
     BigInteger n = BigInteger.Parse(b[0]);
    BigInteger s =BigInteger.Parse(b[1]);
    BigInteger f = s/2;
    if(n>=f){
    Console.WriteLine($"{f}");
    }else{
         Console.WriteLine($"{((s-(2*n))/4)+n}");
    }
 
  }

}