#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using LL = long long;
using pii = pair<int, int>;
#define sz(x) signed(size(x))
using ld = long double;

void solve() {
    int n, m, K, s;
    cin >> n >> m >> K >> s;

    vector<ld> pt(n + m);
    for (auto& i : pt)
        cin >> i;
    sort(pt.begin(), pt.end());

    vector rec(n + m, vector<ld>(n + m));
    for (int l = 0; l < n + m; ++l) {
        ld sum1 = 0, sum2 = 0;
        for (int r = l; r < n + m; ++r) {
            sum1 += pt[r] * pt[r];
            sum2 += pt[r];
            ld mu = sum2;
            rec[l][r] = sum1 - 2 * sum2 * mu / (r - l + 1) + mu * mu / (r - l + 1);
        }
    }

    vector dp(n + m + 1, vector<ld>(K + 1, 1e9));
    dp[0][0] = 0;
    vector pre(n + m + 1, vector<int>(K + 1));
    for (int i = 1; i <= n + m; ++i)
        for (int j = 0; j < i; ++j)
            for (int k = 1; k <= K; ++k) 
                if (dp[j][k - 1] + rec[j][i - 1] < dp[i][k]) {
                    pre[i][k] = j;
                    dp[i][k] = dp[j][k - 1] + rec[j][i - 1];
                }

    ld tmp = (s / 2.0) * (s / 2.0) * (n + m);

    cout << fixed << setprecision(20) << dp[n + m][K] + tmp << '\n';
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    int t = 1;
    while (t--)
        solve();
    return 0;
}