#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int n, m; ll c;
    cin >> n >> m >> c;
    vector<ll> a(n), b(m);
    for (auto &&i : a) scanf("%lld", &i);
    for (auto &&i : b) scanf("%lld", &i);
    sort(a.begin(),a.end(), greater<>());
    sort(b.begin(),b.end());
    ll cnt = 0, cur = 0;
    for (int i = 0; i < n; ++i) {
        while(cur < m && a[i]*b[cur] <= c) cur++;
        cnt += m-cur;
    }
    printf("%.10Lf\n", 1.0L*cnt/n/m);
    return 0;
}