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 Java (OpenJDK 11.0.6) (judge verdict: Wrong Answer)

import java.util.*;
import java.math.BigInteger;
// warm-up
public class Main {

	static void solve() {
		Scanner sc = new Scanner(System.in);
		BigInteger n=sc.nextBigInteger(), m=sc.nextBigInteger(), t=BigInteger.ZERO;
		if (m.doubleValue() < n.doubleValue()) t=m.divide(new BigInteger("2"));
		else {
			t=t.add(n); m=m.subtract(n.multiply(new BigInteger("2")));
			t=t.add(m.divide(new BigInteger("4")));
		}
		System.out.println(t);
		sc.close();			
	}

	public static void main(String args[]) {
		solve();
	}

}