n,m,C=map(int,input().split())
a=list(map(int,input().split()))
b=[0]+list(map(int,input().split()))

b.sort()

def  ni(x):

    def  c(xx):
        return b[xx]*x > C
        
    ng = 0
    ok = m+1
    while ok - ng > 1:
        mid=(ok + ng) // 2
        if c(mid):
            ok = mid
        else:
            ng = mid

    return ng

ans=0

for i in range(n):
    t=ni(a[i])
    ans+= m-t

answer= ans/(n*m)

print(answer)