#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (long long i = 0; i < (n); ++i)
using ll = long long;
using P = pair<ll,ll>;
using vec = vector<ll>;
using vecp = vector<P>;
using mat = vector<vec>;
using matp = vector<vecp>;
const ll MOD = 1e9+7;
const ll INF = 1e18;
#define all(v) v.begin(), v.end()

int main(){
  ll N,M,C,ans=0;
  cin >> N >> M >> C;
  vec A(N),B(M);
  rep(i,N) cin >> A.at(i);
  rep(i,M) cin >> B.at(i);
  sort(all(A));
  sort(all(B));
  rep(i,N){
      ans+=(upper_bound(all(B),C/A.at(i))-B.begin());
  }
  cout << fixed << setprecision(15) << 1.0-(double)ans/double(N*M) << endl;
}