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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;

public class Main{

	static class FastReader{
		BufferedReader br;
		StringTokenizer st;
		public FastReader(){
			br = new BufferedReader(new InputStreamReader(System.in));
		}
		public String next(){
			try{
				while(st==null||!st.hasMoreElements()){
					st = new StringTokenizer(br.readLine());
				}
			}catch(Exception e){
				e.printStackTrace();
			}
			return st.nextToken();
	
		}
		public int nextInt(){
			return Integer.parseInt(next());
		}
		public long nextLong(){
			return Long.parseLong(next());
		}
		public double nextDouble(){
			return Double.parseDouble(next());
		}
		public String nextLine(){
			String s = "";
			try{
				s = br.readLine();
			}catch(Exception e){
				e.printStackTrace();
			}	
			return s;		
		}
	} 
	
	public static void main(String[] args){
		FastReader in = new FastReader();
		PrintWriter out = new PrintWriter(System.out);
		long n = in.nextLong();
		long m = in.nextLong();
		long ans;
		if(n>=m/2){
			ans = m/2;
		}
		else{
			
			ans = (n+m/2)/2;
		}
		out.println(ans);		
		out.flush();
		out.close();  
	}

}