#include <bits/stdc++.h>
#include <atcoder/all>
 
using namespace std;
using namespace atcoder;
 
typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef pair<ll,ll> P;
typedef string str;
typedef vector<P> vp;
typedef vector<str> vs;
typedef map<ll,ll> mp;
typedef set<ll> st;
typedef dsu uf;
typedef fenwick_tree<ll> fw;

const ll mod=1e9+7;
//const ll mod=998244353;
const ll inf=1e18;

#define rep(i,m,n) for(ll i=m;i<n;i++)
#define repr(i,m,n) for(ll i=m-1;i>=n;i--)
#define fi first
#define se second
#define chmax(x,y) x=max(x,y)
#define chmin(x,y) x=min(x,y)
#define eb(x) emplace_back(x)
#define pb(x) pop_back(x)
#define all(x) x.begin(),x.end()
#define allr(x) x.rbegin(),x.rend()
#define lb(x,a) lower_bound(all(x),a)
#define ub(x,a) upper_bound(all(x),a)
#define maxe(x) max_element(all(x))
#define mine(x) min_element(all(x))
#define pc(x) __builtin_popcount(x)
#define np(x) next_permutation(all(x))

void solve(){
  ll n,m,c;
  cin >> n >> m >> c;
  vll a(n),b(m);
  rep(i,0,n) cin >> a[i];
  rep(i,0,m) cin >> b[i];
  
  sort(all(a));
  sort(all(b));
  
  long double ans=0;
  
  rep(i,0,n){
   ll it=b.end()-upper_bound(all(b),c/a[i]); 
   ans+=double(it)/double(m); 
  }
  ans/=n;
  cout << fixed << setprecision(12) << ans << endl;
}
int main(){
   cin.tie(nullptr);
  ios::sync_with_stdio(false);
  solve();
}