use std::io::{self, BufReader, BufWriter, Read, Write};

fn main() {
    let stdin = io::stdin();
    let mut stdin = BufReader::new(stdin.lock());
    let stdout = io::stdout();
    let mut stdout = BufWriter::new(stdout.lock());

    let mut buf = String::new();
    stdin.read_to_string(&mut buf).unwrap();

    let mut iter = buf.split_whitespace();
    let l: u32 = iter.next().unwrap().parse().unwrap();
    let k: u32 = iter.next().unwrap().parse().unwrap();

    let result = l / (2 * k) * k;
    writeln!(&mut stdout, "{}", result).unwrap();
}