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: Time Limit Exceeded)

fn main() {
    use std::io;
    let mut input = String::new();
    let _ = io::stdin().read_line(&mut input);
    let input_nums =
        input.trim().split_whitespace().map(|x| x.parse::<usize>().unwrap()).collect::<Vec<_>>();
    let mut n = input_nums[0];
    let mut m = input_nums[1];
    let mut result = 0;
    loop {
        if n == 0 && m <= 3 {
            break;
        } else if n == 0 && m > 2 {
            n += 1;
            m -= 2;
        } else if n * 2 <= m {
            result = result + n;
            m = m - (n * 2);
            n = 0;
        } else {
            result = result + (m / 2);
            n = n - (m / 2);
            m = m % 2;
        }
    }
    println!("{}", result);
}