#include <bits/stdc++.h>

using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

const int N = 1 << 11;
const db INF = 1e47;

db val[N][N];

int main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout << fixed << setprecision(15);
	int m, n, k, s;
	cin >> m >> n >> k >> s;
	n = n + m;
	vector<db> x(n);
	for (db& xi : x)
		cin >> xi;
	sort(ALL(x));
	FOR(i, 0, n)
	{
		db s0 = 0, s1 = 0, s2 = 0;
		FOR(j, i, n)
		{
			s0 += 1;
			s1 += x[j];
			s2 += x[j] * x[j];
			val[i][j + 1] = -s1 * s1 / s0 + s2;
		}
	}
	vector<db> dp(n + 1, INF), ndp(n + 1);
	dp[0] = 0;
	ndp = dp;
	while (k--)
	{
		FOR(i, 0, n)
		{
			FOR(j, i + 1, n + 1)
			{
				ndp[j] = min(ndp[j], dp[i] + val[i][j]);
			}
		}
		dp = ndp;
	}
	cout << dp[n] + n * s * s / 4.0 << "\n";
	return 0;
}