fn main() {
    let mut xx = String::new();
    std::io::stdin().read_line(&mut xx).ok();
    let xx: Vec<u32> = xx.split_whitespace().flat_map(str::parse).collect();

    let mut answer = 0.;
    for i in 1..=xx[0] {
        answer += f64::from(i);
    }
    answer /= f64::from(xx[0] + 1);

    println!("{}", answer);
}