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.math.BigInteger;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner((System.in));
		BigInteger N = new BigInteger(String.valueOf(sc.next()));
		BigInteger M = new BigInteger(String.valueOf(sc.next()));
		BigInteger m = M.subtract(N.multiply(new BigInteger("2")));
				
		if (m.compareTo(BigInteger.ZERO) == 0) {
			// equal
			System.out.println(N);
			sc.close();
			return;
		} else if (m.compareTo(BigInteger.ZERO) < 0) {
			// n big
			System.out.println(M.divide(new BigInteger("2")));
			sc.close();
			return;
		} else {
			// m big
			System.out.println(N.add(m.divide(new BigInteger("4"))));
		}
		
		sc.close();
	}
}