#include<bits/stdc++.h>
using namespace std;

typedef long long ll;

const int N = 2e3 + 10;

double a[N], sum1[N], sum2[N], cost[N][N], f[N][N];

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    if (fopen("qoj_7691.inp", "r")) {
        freopen("qoj_7691.inp", "r", stdin);
        freopen("qoj_7691.out", "w", stdout);
    }

    #ifdef LOCAL_MACHINE 
        if (fopen("task.inp", "r")) {
            freopen("task.inp", "r", stdin);
            freopen("task.out", "w", stdout);
        }
    #endif

    int m, n, k, s; cin >> m >> n >> k >> s;
    n += m;
    for (int i = 1; i <= n; ++i) cin >> a[i]; 
    sort(a + 1, a + n + 1);

    for (int i = 1; i <= n; ++i) {
        sum1[i] = sum1[i - 1] + a[i];
        sum2[i] = sum2[i - 1] + a[i] * a[i];
    }

    for (int i = 1; i <= n; ++i) for (int j = i; j <= n; ++j) {
        double p = (sum1[j] - sum1[i - 1]) / (j - i + 1);
        cost[i][j] = sum2[j] - sum2[i - 1] + p * p * (j - i + 1) - p * (sum1[j] - sum1[i - 1]) * 2;

        // cout << i << " " << j << " " << p << " " << cost[i][j] << "\n";
    }

    // cout << "\n";

    for (int i = 0; i < N; ++i) for (int j = 0; j < N; ++j) f[i][j] = 1e9;

    f[0][0] = 0;
    for (int j = 1; j <= k; ++j) for (int i = 1; i <= n; ++i) {
        for (int t = 0; t < i; ++t) f[i][j] = min(f[i][j], f[t][j - 1] + cost[t + 1][i]);
        // cout << i << " " << j << " " << f[i][j] << "\n";
    }

    double x = 0.5 * s;

    cout << fixed << setprecision(7) << f[n][k] + n * x * x << "\n";
}

// ඞඞඞඞඞ you sus