import sys
from bisect import bisect_left,bisect_right
sys.setrecursionlimit(10**7)
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


N,M,C = MI()
A = LI()
B = [0]+LI()

ans = 0
for a in A:
    x = (C//a)+1
    index = bisect_left(B,x)
    ans += M-index+1
print(ans/(N*M))