#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;


int main(){
  ll N, M, C;
  cin >> N >> M >> C;
  vector<ll> v;
  rep(i,N){
    ll a;
    cin >> a;
    v.push_back(a);
  }
  map<ll,ll> cnt;
  rep(i,M){
    ll a;
    cin >> a;
    cnt[a]++;
  }

  vector<pair<ll,ll>> w;
  FOR(it,cnt){
    w.emplace_back(it->first, it->second);
  }
  reverse(ALLOF(w));

  vector<pair<ll,ll>> csum;
  ll base = 0;
  rep(i,w.size()){
    base += w[i].second;
    csum.emplace_back(w[i].first, base);
  }
  sort(ALLOF(csum));
  
  double ret = 0;
  rep(i,N){
    if(csum[0].first * v[i] > C){
      ret += (1.0 / N);
    }else{
      int lb = 0, ub = w.size();
      while(ub-lb>1){
        int m = (lb+ub)/2;
        if(csum[m].first * v[i] <= C) lb = m;
        else ub = m;
      }
      if(ub<w.size()){
        ret += (1.0 / N) * csum[ub].second / M;
      }
    }
  }
  
  printf("%.12lf\n", ret);
  
  return 0;
}