n,m,c = map(int, input().split())
a = list(map(int, input().split()))
b = list(map(int, input().split()))
b.sort()
from bisect import bisect_right,bisect_left

res = 0
for aa in a:
    tmp = c//aa
    pos = bisect_right(b,tmp)
    res += pos/(m*n)

print(1-res)