import java.util.*;

public class Main {
	public static void main (String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int k = sc.nextInt();
		long x = sc.nextInt();
		long y = sc.nextInt();
		int[] arr = new int[n];
		for (int i = 0; i < n; i++) {
		    arr[i] = (sc.nextInt() - 1 + k - 1) / k;
		}
		Arrays.sort(arr);
		long sum = arr[n - 1];
		long min = arr[n - 1] * y;
		for (int i = n - 2; i >= 0; i--) {
		    min = Math.min(min, arr[i] * y + (sum - (long)(n - i - 1) * arr[i]) * x);
		    sum += arr[i];
		}
		min = Math.min(min, sum * x);
		System.out.println(min);
	}
}