[n,m,c]=list(map(int,input().split()))
a=list(map(int, input().split()))
b=list(map(int, input().split()))
count=0
s=n*m
for i in range(n):
    for j in range(m):
        x=a[i]*b[j]
        if(x>c):
            count+=1
print(count/s)