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

int main()
{
	int64_t n, k, x, y;
	cin >> n >> k >> x >> y;
	vector<int64_t> as(n);
	for (auto &&a : as)
	{
		cin >> a;
		a--;
	}

	sort(as.begin(), as.end());

	vector<int64_t> bs(n);
	for (int64_t i = 0; i < n; i++)
	{
		bs[i] = (as[i] + k - 1) / k;
	}

	int64_t sum = accumulate(bs.begin(), bs.end(), int64_t(0));

	int64_t ans = min(x * sum, y * *max_element(bs.begin(), bs.end()));
	for (int64_t i = 0, tmp = 0; i < n; i++)
	{
		tmp += bs[i];

		ans = min(ans, y * bs[i] + x * (sum - tmp - bs[i] * (n - i - 1)));
	}

	cout << ans << endl;

	return 0;
}