use std::io::*;
use std::str::FromStr;

fn get_primes(max_prime: i64) -> Vec<i64> {
    let mut ret = Vec::new();
    let mut isprime = vec![true; (max_prime + 1) as usize];
    isprime[0] = false;
    isprime[1] = false;
    for i in 2..(max_prime + 1) as usize {
        if isprime[i] {
            ret.push(i as i64);
            for j in i * 2..(max_prime + 1) as usize {
                isprime[j] = false;
            }
        }
    }
    ret
}

fn zeta(n: i64) -> f64 {
    let primes = get_primes(1000000);
    let mut ret = 1.0;

    for i in 0..primes.len() {
        let p = primes[i] as f64;
        let x = 1.0 / (1.0 - p.powf(-n as f64));
        ret *= x;
    }

    ret
}

fn main() {
    let mut s = String::new();
    stdin().read_line(&mut s).ok();
    let s = s.trim();
    let n = i64::from_str(s).unwrap();

    println!("{:.14}", zeta(n));
}