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::cmp::{max,min};
macro_rules! string2tuple {
    ($l:ident, ($($t:ty),*)) => {{
        let mut ws = $l.split_whitespace();
        (
            $(ws.next().unwrap().parse::<$t>().unwrap(),)*
        )
    }}
}
fn solve(nm: &str) -> i64 {
    let (n,m) = string2tuple!(nm,(i64,i64));
    min(n,m/2)+max(0,(m-n*2)/4)
}
fn main() {
    loop {
        let mut s = String::new();
        std::io::stdin().read_line(&mut s).unwrap();
        let s = s.trim_right();
        if s=="" { break; }
        println!("{}",solve(&s));
    }
}