from math import factorial
import sys
sys.setrecursionlimit(100000)

used1 = []
used2 = []
n = 0
ap = []
bp = []
a, b = ([], [])

def rec2(pos):
    ans = 0
    if pos == n:
        # a, b の勝ち数
        aa, bb = (0, 0)
        for x, y in zip(ap, bp):
            if a[x] > b[y]:
                aa += 1
            elif a[x] < b[y]:
                bb += 1
        return 1 if aa > bb else 0
    for i in range(n):
        if not used2[i]:
            bp.append(i)
            used2[i] = True
            ans += rec2(pos+1)
            used2[i] = False
            bp.pop()
    return ans


def rec1(pos):
    ans = 0
    if pos == n:
        # return rec2(0, a, b)
        return rec2(0)
    for i in range(n):
        if not used1[i]:
            used1[i] = True
            ap.append(i)
            ans += rec1(pos+1)
            ap.pop()
            used1[i] = False
    return ans


def main():
    global used1, used2, n, a, b
    n = int(input())
    used1 = [False for i in range(n)]
    used2 = [False for i in range(n)]
    a = [int(i) for i in input().split()]
    b = [int(i) for i in input().split()]
    print(rec1(0)/factorial(n)**2)


if __name__ == '__main__':
    main()