import time
import random

n, pa, pb = map(float, input().split())
n = int(n)
A = list(map(int, input().split()))
B = list(map(int, input().split()))
A.sort()
B.sort()

nume = 0
deno = 0
start = time.time()
while time.time() - start < 2.0:
    score = 0
    remA = [True] * n
    remB = [True] * n
    for i in range(n):
        if i == n - 1:
            WA = [1 if tf else 0 for tf in remA]
            WB = [1 if tf else 0 for tf in remB]
        else:
            pa_ = (1.0 - pa) / (n - i - 1)
            pb_ = (1.0 - pb) / (n - i - 1)
            WA = [pa_ if tf else 0 for tf in remA]
            WB = [pb_ if tf else 0 for tf in remB]
            WA[remA.index(True)] = pa
            WB[remB.index(True)] = pb
        a = random.choices(range(n), WA)[0]
        b = random.choices(range(n), WB)[0]
        if A[a] > B[b]:
            score += A[a] + B[b]
        else:
            score -= A[a] + B[b]
        remA[a] = False
        remB[b] = False
    if score > 0:
        nume += 1
    deno += 1

print(nume / deno)