#include <iostream>
#include <cstdint>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
	cin.tie(nullptr);
	ios::sync_with_stdio(false);

	uint32_t N, K, X, Y, i;
	cin >> N >> K >> X >> Y;
	vector<uint32_t> A(N);
	for (i = 0; i != N; ++i) cin >> A[i];

	sort(A.begin(), A.end());
	uint32_t HP = 1;
	uint64_t ans = 0;
	for (i = 0; i != N; ++i)
	{
		if (HP >= A[i]) continue;

		if (X * static_cast<uint64_t>(N - i) < Y)
			ans += (A[i] - HP + K - 1) / K * (X * static_cast<uint64_t>(N - i));
		else
			ans += (A[i] - HP + K - 1) / K * static_cast<uint64_t>(Y);

		HP += (A[i] - HP + K - 1) / K * K;
	}

	cout << ans << '\n';
	return 0;
}