#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  ll n, m, c;
  cin >> n >> m >> c;
  vector<ll> a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  sort(a.begin(), a.end());
  sort(b.begin(), b.end());
  ll ans = 0;
  rep(i, n) {
    ans += b.end() - upper_bound(b.begin(), b.end(), c / a[i]);
  }
  // cout << ans << ' ' << n * m << '\n';
  ll g = gcd(ans, n * m);
  cout << fixed << setprecision(15) << (double) (ans / g) / (double) (n * m / g) << '\n';
  return 0;
}