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)

fn getline() -> String {
    let mut __ret = String::new();
    std::io::stdin().read_line(&mut __ret).ok();
    return __ret;
}

fn solve(s: i64, c: i64) -> i64 {
    if c <= 1 {
        return 0;
    }

    if s * 2 >= c {
        return c/2;
    }


    // s*2 < c の場合
    // s個は絶対作る。残りのパーツでできるだけsccを作る
    let ans = s + (c - s * 2) / 4;
    return ans;
}

fn main() {
    let s = getline();
    let vec: Vec<i64> = s.trim().split(' ').map(|s| s.parse().unwrap()).collect();
    let s = vec[0];
    let c = vec[1];

    let ans = solve(s, c);
    println!("{}", ans);
}