#include<stdio.h>
long long int h[100005], l;
int comp_h(int long long a, int long long b)
{
	if (h[a] > h[b])
		return 1;
	else
		return -1;
}
void swap_h(long long int a, long long int b)
{
	long long int f = h[a];
	h[a] = h[b];
	h[b] = f;
	return;
}
void push(long long int ne)
{
	h[l] = ne;
	long long int p = l;
	l++;
	for (; p > 0; p = (p - 1) / 2)
		if (comp_h((p - 1) / 2, p) > 0)
			swap_h((p - 1) / 2, p);
	return;
}
long long int pop()
{
	l--;
	swap_h(0, l);
	long long int p = 0;
	for (;;)
	{
		if (2 * p + 2 < l)
		{
			if (comp_h(2 * p + 1, 2 * p + 2) > 0)
			{
				if (comp_h(p, 2 * p + 2) > 0)
					swap_h(p, 2 * p + 2);
				p = 2 * p + 2;
			}
			else
			{
				if (comp_h(p, 2 * p + 1) > 0)
					swap_h(p, 2 * p + 1);
				p = 2 * p + 1;
			}
		}
		else if (2 * p + 1 < l)
		{
			if (comp_h(p, 2 * p + 1) > 0)
				swap_h(p, 2 * p + 1);
			p = 2 * p + 1;
		}
		else
			break;
	}
	return h[l];
}
long long int a[100005], b[100005];
int main()
{
	long long int n, m, c;
	scanf("%lld %lld %lld", &n, &m, &c);
	int i, j;
	for (i = 0; i < n; i++)
		scanf("%lld", &a[i]);
	for (i = 0; i < m; i++)
		scanf("%lld", &b[i]);
	l = 0;
	for (i = 0; i < n; i++)
		push(a[i]);
	for (i = 0; i < n; i++)
		a[i] = pop();
	l = 0;
	for (i = 0; i < m; i++)
		push(b[i]);
	for (i = 0; i < m; i++)
		b[i] = pop();
	long long int cnt = 0;
	b[m] = c + 1;
	for (i = 0, j = m; i < n; i++)
	{
		if (j == m && a[i] * b[m - 1] > c)
			j--;
		if (j < m)
		{
			while (a[i] * b[j] > c)
			{
				j--;
				if (j < 0)
					break;
			}
			j++;
		}
		cnt += m - j;
	}
	printf("%.20lf\n", cnt / (double)(n * m));
	return 0;
}