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 Java7 (OpenJDK 1.7.0) (judge verdict: Wrong Answer)

import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Stack;


public class Main {

	/**
	 * @param args
	 */
	
	
	public static void main(String[] args) {
		
		
		
		Scanner sc= new Scanner(System.in);
	
	
		long n=sc.nextLong();
		long m=sc.nextLong();
		
		long ans=0;
		
		if(2*n<=m)
		{
			ans+=n;
			m-=2*n;
		    ans+=m/4;		
		}
		else 
		{
		if(m%2!=0)	
		{
		ans=m-1;	
		}
		else 
		{
		ans=m;	
		}
		}
	System.out.println(ans);	
			
}
}