#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);

    ll N,M,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());

    double cnt = 0;
    for(auto a : A){
        ll x = C / a;
        cnt += B.end() - upper_bound(B.begin(), B.end(), x);
    }
    cnt /= N;
    cnt /= M;
    cout.precision(17);
    cout << cnt << '\n';
}