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 Rust (1.15.1) (judge verdict: Accepted)

use std::io;

fn main() {
    let (n, m) = {
        let mut line = String::new();
        io::stdin().read_line(&mut line).unwrap();
        let nm = line.split_whitespace().map(|s| s.parse().unwrap()).collect::<Vec<i64>>();
        (nm[0], nm[1])
    };

    let a = if m > n * 2 {
        let x = m - n * 2;
        x / 4 + n
    } else {
        m / 2
    };

    print!("{:?}", a);
}