// ---------- begin input macro ----------
// reference: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};
    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };
    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };
    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };
    ($iter:expr, bytes) => {
        read_value!($iter, String).bytes().collect::<Vec<u8>>()
    };
    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };
    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}
// ---------- end input macro ----------

fn run() {
    input! {
        n: usize,
        a: [u32; n],
        b: [u32; n],
    }
    let a = a.into_iter().enumerate().map(|p| (p.1, p.0)).collect::<Vec<_>>();
    let mut ans = 0f64;
    let p = 0.5f64;
    for (i, &x) in a.iter().enumerate() {
        let mut dp = vec![1f64];
        for &y in a.iter().take(i) {
            let mut next = vec![0f64; dp.len() + 1];
            if y < x {
                for (i, &dp) in dp.iter().enumerate() {
                    next[i] += p * dp;
                    next[i + 1] += p * dp;
                }
            } else {
                for (i, &dp) in dp.iter().enumerate() {
                    next[i] += p * dp;
                    next[i.saturating_sub(1)] += p * dp;
                }
            }
            dp = next;
        }
        ans += dp[0] * p * b[i] as f64 * x.0 as f64;
        let mut next = vec![0f64; dp.len() + 1];
        for (i, &dp) in dp.iter().enumerate() {
            next[i] += p * dp;
            if i > 0 {
                next[i - 1] += p * dp;
            }
        }
        dp = next;
        for (&y, &b) in a[(i + 1)..].iter().zip(b[(i + 1)..].iter()) {
            if y > x {
                ans += dp[0] * p * b as f64 * x.0 as f64;
            }
            let mut next = vec![0f64; dp.len() + 1];
            if y < x {
                for (i, &dp) in dp.iter().enumerate() {
                    next[i] += p * dp;
                    next[i + 1] += p * dp;
                }
            } else {
                for (i, &dp) in dp.iter().enumerate() {
                    next[i] += p * dp;
                    if i > 0 {
                        next[i - 1] += p * dp;
                    }
                }
            }
            dp = next;
        }
    }
    println!("{:.8}", ans);
}

fn main() {
    run();
}