use std::io::stdin;
pub fn main() {
    let (l, k): (u64, u64) = {
        let mut s = String::new();
        let _ = stdin().read_line(&mut s);
        let mut v = s.split_whitespace().flat_map(|x| x.parse());
        (v.next().unwrap(), v.next().unwrap())
    };
    let mut haruka = 0;
    let mut yu = 0;
    while haruka + yu < l {
        haruka += k;
        if haruka + yu + k < l {
            yu += k;
        }
    }
    println!("{}", yu);
}