#include <algorithm>
#include <cmath>
#include <cstdio>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>

using namespace std;

typedef long long ll;

#define MOD 1000000007

int main() {
  int n, m;
  cin >> n >> m;
  ll c;
  cin >> c;
  vector<ll> a(n), b(m + 1);
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  b[0] = 0;
  for (int i = 1; i <= m; ++i) {
    cin >> b[i];
  }
  sort(b.begin(), b.end());
  double win = 0;
  for (int i = 0; i < n; ++i) {
    int ok = m, ng = 1;
    if (c < a[i] * b[ng]) {
      win += m;
    } else if (a[i] * b[ok] <= c) {
      win += 0;
    } else {
      while (1 < (ok - ng)) {
        int mid = (ok + ng) / 2;
        if (c < a[i] * b[mid]) {
          ok = mid;
        } else {
          ng = mid;
        }
      }
      win += m - ng;
    }
  }
  printf("%.15f\n", win / (1ll * n * m));
  return 0;
}