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: Wrong Answer)

fn main(){
    let mut line = String::new();
    let stdin = std::io::stdin();
    stdin.read_line(&mut line).expect("Could not read line");;
    let p : Vec<_> = line.trim().split(' ').collect();
    let mut n : i64 = p[0].parse().unwrap();
    let mut m : i64 = p[1].parse().unwrap();
    let mut ret : i64 = 0;
    if n >= m / 2 {
        ret = m / 2;
    }
    else {
        while m / 2 > n + 1{
            n += 1;
            m -= 2;
            ret = n;
        }
    }
    println!("{}", ret);
}