#include<bits/stdc++.h>
#include <atcoder/all>
#ifdef LOCAL
#include <debug_print.hpp>
#define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (static_cast<void>(0))
#endif
using namespace atcoder;
using mint=modint998244353;
using namespace std;
using ll=long long;
using ul=unsigned long long;
int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1};
int dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};
using Graph=vector<vector<int>>;
ll op(ll a,ll b){return max(a,b);}
ll e(){return 0;}
int main(){
    double N,M,cnt=0;
    ll C;
    cin>>N>>M>>C;
    vector<ll>A(N),B(M);
    for(int i=0;i<N;i++)cin>>A[i];
    for(int i=0;i<M;i++)cin>>B[i];
    sort(B.begin(),B.end());
    for(int i=0;i<N;i++){
        cnt+=M-(upper_bound(B.begin(),B.end(),C/A[i])-B.begin());
    }
    cout<<fixed<<setprecision(10)<<cnt/(M*N)<<endl;
}