import sys
def S(): return sys.stdin.readline().rstrip()
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 LS(): return list(sys.stdin.readline().rstrip().split())

n,m,c = MI()
a = sorted(LI())
b = sorted(LI())
j = m-1
cnt = 0

for i in range(n):
    cnt += m-1-j
    while j >= 0:
        if a[i]*b[j] > c:
            cnt += 1
            j -= 1
        else:
            break

print(cnt/(m*n))