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 get_line() -> String {
    let mut buf = String::new();
    io::stdin().read_line(&mut buf).ok();
    buf
}

fn main () {
    let nm = get_line().split_whitespace().map( |s| s.parse().unwrap() ).collect::<Vec<u64>>();
    let n = nm[0]; let m = nm[1];
    println!("{}", solve(n,m));
}

fn solve(n:u64, m:u64) -> u64 {
    if n*2 > m { // enough s's
        m / 2
    } else {
        let rem = m - n*2;
        n + (rem / 4)
    }
}