#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::collections::HashMap;
use std::collections::HashSet;

#[allow(unused_macros)]
macro_rules! read {
    ([$t:ty] ; $n:expr) =>
        ((0..$n).map(|_| read!([$t])).collect::<Vec<_>>());
    ($($t:ty),+ ; $n:expr) =>
        ((0..$n).map(|_| read!($($t),+)).collect::<Vec<_>>());
    ([$t:ty]) =>
        (rl().split_whitespace().map(|w| w.parse().unwrap()).collect::<Vec<$t>>());
    ($t:ty) =>
        (rl().parse::<$t>().unwrap());
    ($($t:ty),*) => {{
        let buf = rl();
        let mut w = buf.split_whitespace();
        ($(w.next().unwrap().parse::<$t>().unwrap()),*)
    }};
}

#[allow(dead_code)]
fn rl() -> String {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).unwrap();
    buf.trim_end().to_owned()
}

trait IteratorExt: Iterator + Sized {
    fn vec(self) -> Vec<Self::Item> {
        self.collect()
    }
}
impl<T: Iterator> IteratorExt for T {}

fn main() {
    let n = read!(usize);
    let a = read!([isize]);
    let b = read!([isize]);
    
    println!("{}", help(make_table(a, b), n).iter().filter(|&&e| e > 0).count() as f64 / fact(n) as f64);
}

fn fact(n: usize) -> usize {
    let mut tmp = 1;
    for i in 2..=n {
        tmp *= i;
    }
    tmp
}

fn c(a: isize, b: isize) -> isize {
    if a > b { 1 }
    else { -1 }
}

fn make_table(a: Vec<isize>, b: Vec<isize>) -> Vec<Vec<isize>> {
    let mut v = vec![];
    for eb in b.iter() {
        let mut row = vec![];
        for ea in a.iter() {
            row.push(c(*ea, *eb));
        }
        v.push(row);
    }
    v
}

fn help(table: Vec<Vec<isize>>, size: usize) -> Vec<isize> {
    if size == 1 {
        return vec![table[0][0]];
    }

    let mut v = vec![];
    for i in 0..=size-1 {
        let mut arg_v = table.clone();
        arg_v.remove(0);
        for row in arg_v.iter_mut() {
            row.remove(i);
        }

        for e in help(arg_v, size-1).iter() {
            v.push(e + table[0][i]);
        }
    }
    v
}