import sys, math

def main():
    N = int(sys.stdin.readline())
    p = list(map(float, sys.stdin.readline().split()))
    q = list(map(float, sys.stdin.readline().split()))
    A = list(map(int, sys.stdin.readline().split()))
    l, r = 0.0, 1.0
    for i in range(60):
        mid = (l + r) / 2
        result = mid
        for i in range(N):
            result -= p[i] * (1 - q[i]) / (1 - q[i] * mid)
        if result < 0.0:
            l = mid
        else:
            r = mid
    result = 0.0
    for i in range(N):
        result += A[i] * math.log((1 - q[i]) / (1 - q[i] * l))
    print('{:.12f}'.format(result))

if __name__ == '__main__':
    main()