#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

int main(){
    ll n,m;
    ll c;
    cin >> n >> m >> c;
    vector<ll> a(n),b(m);
    rep(i,n) cin >> a[i];
    rep(i,m) cin >> b[i];
    sort(b.begin(),b.end());

    ll sum = 0;
    rep(i,n){
        int l = -1,r = m;
        while(r - l > 1){
            int mid = (l + r)/2;
            if(a[i] * b[mid] > c) r = mid;
            else l =  mid;
        }
        sum += r;
    }
    sum = n * m - sum;
    cout << setprecision(20) << sum /(double) (n * m ) << endl;
    return 0;
}