import sys
input=sys.stdin.readline
def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))


N,M,C=MI()
A=LI()
B=LI()
A.sort()
B.sort()

def count(a):
    # a*biがCを超えるようなbiの個数を求める
    ng=-1
    ok=M
    while ok-ng>1:
        med=(ok+ng)//2
        if B[med]*a>C:
            ok=med
        else:
            ng=med
    # print(a,M-ok)
    return M-ok

import bisect

ans=0
for i in range(N):
    a=A[i]
    ans+=count(a)


ans=ans/(N*M)

print(ans)