#include <bits/stdc++.h>

using namespace std;
#define int long long
const int MOD = 1000000007;

signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N, K, X, Y;
	cin >> N >> K >> X >> Y;
	vector<int> A(N);
	int sum = 0;
	for (int i = 0; i < N; i++) {
		cin >> A[i];
		A[i] = (A[i] - 1 + K - 1) / K;
		sum += A[i];
	}
	sort(A.begin(), A.end());
	int res = (int)1 << 60;
	int l = 0;
	int c = 0;
	res = sum * X;
	for (int i = 0; i < N; i++) {
		sum -= (A[i] - l) * (N - i);
		res = min(res, sum * X + A[i] * Y);

		l = A[i];
	}
	cout << res << endl;
}