/* 方針
 A君とB君のカードの出し方を順列でそれぞれ調べる.
 A君が勝つ回数を数える
 出し方は全部で (A君の出し方の種類) * (B君の出し方の種類) 通り
 */

yukicoder133()
func yukicoder133() {
    let N = Int(readLine()!)!
    let As: [Int] = readLine()!.split(separator: " ").map { Int($0)! }
    let Bs: [Int] = readLine()!.split(separator: " ").map { Int($0)! }
    
    let permA: [[Int]] = kPermutation(As, k: N)
    let permB: [[Int]] = kPermutation(Bs, k: N)

    var gameWinA = 0
    permA.forEach { gameA in
        permB.forEach { gameB in
            var winA = 0
            for i in 0..<N {
                let (a, b) = (gameA[i], gameB[i])
                if a > b { winA += 1 }
            }
            if winA > N/2 { gameWinA += 1 }
        }
    }
    let ways = permA.count * permB.count
    print(Double(gameWinA) / Double(ways))
}
// k-順列を得る関数
func kPermutation<Element>(_ elements: [Element], k: Int) -> [[Element]] {
    var ret = [[Element]]()
    let n = elements.count
    var used: [Bool] = Array(repeating: false, count: n)

    func dfs(_ seq: [Element]) {
        if seq.count == k {
            ret.append(seq)
            return
        }

        for i in 0..<n {
            if used[i] { continue }
            used[i] = true
            dfs(seq + [elements[i]])
            used[i] = false
        }
    }
    
    dfs([])
    return ret
}