#include "bits/stdc++.h"

#define MOD 1000000007
#define rep(i, n) for(ll i=0; i < (n); i++)
#define rrep(i, n) for(ll i=(n)-1; i >=0; i--)
#define ALL(v) v.begin(),v.end()
#define rALL(v) v.rbegin(),v.rend()
#define FOR(i, j, k) for(ll i=j;i<k;i++)
#define debug_print(var) cerr << #var << "=" << var <<endl;
#define DUMP(i, v)for(ll i=0;i<v.size();i++)cerr<<v[i]<<" "
#define fi first
#define se second

using namespace std;
typedef long long int ll;
typedef vector<ll> llvec;
typedef vector<double> dvec;
typedef pair<ll, ll> P;
typedef long double ld;
struct edge{ll x, c;};

/**************************************
** A main function starts from here  **
***************************************/
int main(){
  ll N, M, C;
  cin >> N >> M >> C;
  llvec a(N), b(M);
  rep(i, N)cin >> a[i];
  rep(i, M)cin >> b[i];
  sort(ALL(a));
  sort(ALL(b));
  ld ans = 0;
  rep(i, N){
    ll tmp = b.end() - upper_bound(ALL(b), C/a[i]);
    ans += (ld)tmp/N/M;
  }
  cout << setprecision(15)<<ans << endl;
  return 0;
}