use std::io::Read;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();
    let mut iter = buf.split_whitespace();

    let n: i32 = iter.next().unwrap().parse().unwrap();
    let k: i32 = iter.next().unwrap().parse().unwrap();

    if n % 2 == 0 {
        println!("{}", std::cmp::min(k * 2, n / 2));
    } else {
        println!("{}", std::cmp::min(k * 2, n));
    }
}