use itertools::{Itertools, iproduct};
use proconio::input;

// https://maguro.dev/blog/debug-macro/
#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),* $(,)*) => {
        #[cfg(debug_assertions)]
        eprintln!(concat!($("| ", stringify!($a), " = {:?} "),*, "|"), $(&$a),*);
    };
}

fn main() {
    input! {
        n: usize,
        a: [usize; n],
        b: [usize; n]
    }

    let mut all = 0;
    let mut win = 0;
    for (u, v) in iproduct!(a.iter().permutations(n), b.iter().permutations(n)) {
        let mut cnt = 0;
        for i in 0..n {
            if u[i] > v[i] {
                cnt += 1;
            }
        }

        win += (n / 2 < cnt) as usize;
        all += 1;
    }

    debug!(all, win);
    let res = (win as f64) / (all as f64);
    println!("{res}");
}