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)

/// 1行の文字を空白で分割してVec<T>にする。
fn read_split<T : std::str::FromStr>() -> Vec<T> {
    let mut input = String::new();
    std::io::stdin().read_line(&mut input).unwrap();
    input.trim().split_whitespace().map(|x| x.parse().ok().unwrap()).collect()
}


fn main() {
    let input : Vec<i64> = read_split();
    let vec_n = input[0];
    let vec_m = input[1];
    if vec_n * 2 > vec_m {
        println!("{}", vec_m / 2);
        return;
    }
    let vec_m = vec_m - (vec_n * 2);

    println!("{}", vec_n + (vec_m / 4));
}