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: Runtime Error)

import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner scan = new Scanner(System.in);
        int N = scan.nextInt(); // S piece
        int M = scan.nextInt(); // C piece
        
        for(int i = 1; i <= N; i++) {
            if(i * 2  < M) {
                continue;
            } else {
                System.out.println(i - 1);
                return;
            }
        }
        
        for(int i = N; i <= N + M / 2; i++) {
            if(i * 2  < M - (i - N) * 2) {
                continue;
            } else {
                System.out.println(i - 1);
                return;
            }
        }
        
        System.out.println(0);
    }
}