fn main() {
    let p = read::<f64>();
    println!("{}", 1.0 / (1.0 - p) - 1.0);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}