#line 1 "/workspaces/compro/lib/template.hpp"


#line 1 "/workspaces/compro/lib/io/vector.hpp"
#include <iostream>
#include <vector>

#ifndef IO_VECTOR
#define IO_VECTOR

template <class T> std::ostream &operator<<(std::ostream &out, const std::vector<T> &v) {
  int size = v.size();
  for (int i = 0; i < size; i++) {
    std::cout << v[i];
    if (i != size - 1)
      std::cout << " ";
  }
  return out;
}

template <class T> std::istream &operator>>(std::istream &in, std::vector<T> &v) {
  for (auto &el : v) {
    std::cin >> el;
  }
  return in;
}

#endif
#line 4 "/workspaces/compro/lib/template.hpp"
#include <bits/stdc++.h>
#define REP(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define ALL(v) (v).begin(), (v).end()
#define coutd(n) cout << fixed << setprecision(n)
#define ll long long int
#define vl vector<ll>
#define vi vector<int>
#define MM << " " <<

using namespace std;

template <class T> void say(bool val, T yes, T no) { cout << (val ? yes : no) << "\n"; }

void say(bool val, string yes = "Yes", string no = "No") { say<string>(val, yes, no); }

template <class T> void chmin(T &a, T b) {
  if (a > b)
    a = b;
}

template <class T> void chmax(T &a, T b) {
  if (a < b)
    a = b;
}

// C++ 17に完全移行したら消す
// 最大公約数を求める
template <class T> T gcd(T n, T m) { return n ? gcd(m % n, n) : m; }

// 最小公倍数を求める
template <class T> T lcm(T n, T m) {
  int g = gcd(n, m);
  return n * m / g;
}

// 重複を消す。計算量はO(NlogN)
template <class T> void unique(std::vector<T> &v) {
  std::sort(v.begin(), v.end());
  v.erase(std::unique(v.begin(), v.end()), v.end());
}


#line 2 "main.cpp"

double solve(ll N, ll M, long long C, const std::vector<long long> &a, const std::vector<long long> &b) {
  ll ret = 0;
  REP(i, N) {
    ll ok = 2e9;
    ll ng = 0;
    while (abs(ok - ng) > 1) {
      ll mid = (ok + ng) / 2;
      if (a[i] * mid > C) {
        ok = mid;
      } else {
        ng = mid;
      }
    }
    ret += distance(lower_bound(ALL(b), ok), b.end());
  }
  return (double)ret / (N * M);
}

// generated by online-judge-template-generator v4.7.1 (https://github.com/online-judge-tools/template-generator)
int main() {
  long long N, M;
  long long C;
  std::cin >> N;
  std::vector<long long> a(N);
  std::cin >> M;
  std::vector<long long> b(M);
  std::cin >> C;
  for (int i = 0; i < N; ++i) {
    std::cin >> a[i];
  }
  for (int i = 0; i < M; ++i) {
    std::cin >> b[i];
  }
  sort(ALL(a));
  sort(ALL(b));
  auto ans = solve(N, M, C, a, b);
  std::coutd(10) << ans << std::endl;
  return 0;
}