#include <bits/stdc++.h>

using namespace std;
using ll = long long;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    ll N, M, C, ans=0;
    cin >> N >> M >> C;
    vector<ll> a(N), b(M);
    for (int i=0; i<N; i++) cin >> a[i];
    for (int j=0; j<M; j++) cin >> b[j];
    sort(b.begin(), b.end());

    for (int i=0; i<N; i++){
        //a*b<=c
        //b<=c/a
        ans += upper_bound(b.begin(), b.end(), C/a[i])-b.begin();
    }

    cout << setprecision(18) << 1.0l-(long double)(ans)/(long double)(N*M) << endl;

    return 0;
}