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: Wrong Answer)

import java.io.*;
import java.util.*;
public class Main {
    private static MyScanner scanner;

    public static void main (String[] args){
        Main instance = new Main();
        scanner = instance.new MyScanner();
        instance.solve();
    }

    private void solve() {
        try {
            int counter = 0;
            Long N = scanner.nextLong();
            Long M = scanner.nextLong();
            if (M >= 2*N) {
                counter += N;
                M -= 2*N;
                N -= N;
            } else {
                counter += M / 2;
                M -= M / 2;
            }
            if (M > 3) {
                counter += M / 4;
            }
            System.out.println(counter);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private class MyScanner {
        String[] s;
        int i;
        BufferedReader br;
        String reg = " ";

        MyScanner () {
            s = new String[0];
            i = 0;
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        public String next() throws IOException {
            if (i < s.length) return s[i++];
            String line = br.readLine();
            while (line.equals("")) {
                line = br.readLine();
            }
            s = line.split(reg, 0);
            i = 0;
            return s[i++];
        }

        public int nextInt() throws NumberFormatException, IOException {
            return Integer.parseInt(next());
        }

        public double nextDouble() throws NumberFormatException, IOException {
            return Double.parseDouble(next());
        }

        public long nextLong() throws NumberFormatException, IOException {
            return Long.parseLong(next());
        }
    }
}