#include <bits/stdc++.h>
using namespace std;
int main(){
  cout << fixed << setprecision(10);
  int N, M;
  long long C;
  cin >> N >> M >> C;
  vector<long long> a(N);
  for (int i = 0; i < N; i++){
    cin >> a[i];
  }
  vector<long long> b(M);
  for (int i = 0; i < M; i++){
    cin >> b[i];
  }
  sort(a.begin(), a.end());
  sort(b.begin(), b.end());
  long long sum = 0;
  for (int i = 0; i < N; i++){
    int tv = M;
    int fv = -1;
    while (tv - fv > 1){
      int mid = (tv + fv) / 2;
      if (a[i] * b[mid] > C){
        tv = mid;
      } else {
        fv = mid;
      }
    }
    sum += M - tv;
  }
  cout << (double) sum / N / M << endl;
}