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::{self, BufRead};
use std::str::FromStr;

fn main() {
    let stdin = io::stdin();
    let line = stdin.lock().lines().next().unwrap().unwrap();
    let ints: Vec<u64> = line.split(' ').map(|s| u64::from_str(s).unwrap()).collect();
    let s = ints[0];
    let c = ints[1];

    if s >= c/2 {
        println!("{}", c/2);
    } else {
        let scc = s;
        let c_rest = c - scc*2;
        println!("{}", scc + c_rest/4);
    }
}