#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using P = pair<int, int>;
using PL = pair<lint, lint>;
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
#define ALL(a)  (a).begin(),(a).end()
constexpr int MOD = 1000000007;
constexpr lint B1 = 1532834020;
constexpr lint M1 = 2147482409;
constexpr lint B2 = 1388622299;
constexpr lint M2 = 2147478017;
constexpr int INF = 2147483647;
void yes(bool expr) {cout << (expr ? "Yes" : "No") << "\n";}
template<class T>void chmax(T &a, const T &b) { if (a<b) a=b; }
template<class T>void chmin(T &a, const T &b) { if (b<a) a=b; }
int main()
{
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  lint N, M, C;
  cin >> N >> M >> C;
  vector<lint> a(N);
  REP(i, N) cin >> a[i];
  vector<lint> b(M);
  REP(i, M) cin >> b[i];
  sort(ALL(b));
  lint cnt = 0;
  REP(i, N) {
    lint l = -1;
    lint r = M;
    while(r-l > 1) {
      lint m = (l+r) / 2;
      if(a[i]*b[m] > C) r = m;
      else l = m;
    }
    cnt += M-r;
    //cout << cnt << endl;
  }
  double ans = (double)cnt / (double) M / (double)N;
  cout << fixed << setprecision(10) << ans << "\n";
}