fn main() {
    let mut k = String::new();
    std::io::stdin().read_line(&mut k).ok();
    let k: usize = k.trim().parse().unwrap();

    let mut result = 0.;
    for n in 1..100000000 {
        result += 1. / (n as f64) / (n + k) as f64;
    }
    println!("{:.09}", result);
}