#pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
using namespace std;

#ifdef WAIMAI
#define debug(HEHE...) cout << "[" << #HEHE << "] : ", dout(HEHE)
void dout() {cout << '\n';}
template<typename T, typename...U>
void dout (T t, U...u) {cout << t << (sizeof... (u) ? ", " : ""), dout (u...);}
#else
#define debug(...) 7122
#endif

#define ll long long
#define Waimai ios::sync_with_stdio(false), cin.tie(0)
#define FOR(x,a,b) for (int x = a, I = b; x <= I; x++)
#define pb emplace_back
#define F first
#define S second

const int SIZE = 2005;
const double INF = 9e18;

int n, m, k;
double s, x[SIZE];
double p1[SIZE], p2[SIZE];
double dp[SIZE][105], val[SIZE][SIZE];

double cal(int l, int r) {
    double mid = (p1[r] - p1[l - 1]) / (r - l + 1);
    return (p2[r] - p2[l - 1]) - 2 * mid * (p1[r] - p1[l - 1]) + (r - l + 1) * mid * mid;
}

void solve() {
    cin >> n >> m >> k >> s;
    n += m;
    FOR (i, 1, n) cin >> x[i];
    sort(x + 1, x + n + 1);
    FOR (i, 1, n) {
        p1[i] = p1[i - 1] + x[i];
        p2[i] = p2[i - 1] + x[i] * x[i];
    }

    dp[0][0] = n * s * s / 4;
    fill(dp[0] + 1, dp[0] + k + 1, INF);
    FOR (i, 1, n) FOR (j, i, n) val[i][j] = cal(i, j);
    FOR (i, 1, n) {
        fill(dp[i], dp[i] + k + 1, INF);
        FOR (j, 0, i - 1) FOR (t, 1, k) dp[i][t] = min(dp[i][t], dp[j][t - 1] + val[j + 1][i]);
    }
    cout << fixed << setprecision(10) << dp[n][k] << '\n';
}

int main() {
    Waimai;
    solve();
}