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.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.util.InputMismatchException;

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            solve(in);
        }
    }

    private static void solve(Scanner in) {
        long N = in.nextLong(), M = in.nextLong();
        long ans = 0;
        if (N >= M / 2) {
            ans = M / 2;
        } else {
            ans = N;
            long rem = M - N * 2;
            ans += (rem / 4);
        }
        System.out.println(ans);
    }
}

class Scanner implements Closeable {
    private final InputStream stream;
    private final byte[] buf = new byte[1024];
    private int cur;
    private int num;

    Scanner(InputStream stream) {
        this.stream = stream;
    }

    int[] nextIntArray(int n) {
        int[] a = new int[n];
        for (int i = 0; i < n; i++)
            a[i] = nextInt();
        return a;
    }

    int nextInt() {
        return (int) nextLong();
    }

    long nextLong() {
        int c = read();
        while (isdel(c))
            c = read();
        int sgn = 1;
        if (c == '-') {
            sgn = -1;
            c = read();
        }
        long l = 0;
        do {
            if (c < '0' || c > '9')
                throw new InputMismatchException();
            l *= 10;
            l += c - '0';
            c = read();
        } while (!isdel(c));
        return l * sgn;
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    String next() {
        int c = read();
        while (isdel(c))
            c = read();
        StringBuilder s = new StringBuilder();
        do {
            s.appendCodePoint(c);
            c = read();
        } while (!isdel(c));
        return s.toString();
    }

    private int read() {
        if (num == -1)
            throw new InputMismatchException();
        if (cur >= num) {
            cur = 0;
            try {
                num = stream.read(buf);
            } catch (Exception e) {
                throw new InputMismatchException();
            }
            if (num <= 0)
                return -1;
        }
        return buf[cur++];
    }

    private boolean isdel(int c) {
        return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
    }

    @Override
    public void close() {
        try {
            stream.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}