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)

#![allow(non_snake_case,unused_variables,dead_code)]
use std::io::{self, BufRead};
use std::str;

fn main() {
    let stdin = io::stdin();
    let mut s = String::new();
    let _ = stdin.read_line(&mut s);
    let vec: Vec<i64> = s.split_whitespace().map(|v| str::parse::<i64>(v).unwrap()).collect();

    let mut N = vec[0];
    let mut M = vec[1];

    let mut res = 0;
    while N * 2 <= M && N > 0 {
        N -= 1;
        M -= 2;
        res += 1;
    }
    res += M / 4;
    println!("{}", res);
}