using System;

public class Hello
{
    static int n, k, x, y, azero;
    static long ans;

    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        n = int.Parse(line[0]);
        k = int.Parse(line[1]);
        x = int.Parse(line[2]);
        y = int.Parse(line[3]);
        var a = new int[n];
        line = Console.ReadLine().Trim().Split(' ');
        azero = 0;
        for (int i = 0; i < n; i++)
        {
            a[i] = (int.Parse(line[i]) + k - 2) / k;
            if (a[i] == 0) azero++;
        }
        ans = 0L;
        getAns(a);
        Console.WriteLine(ans);
    }
    static void getAns(int[] a)
    {
        while (azero < n)
        {
            if (check(a)) { ans += (long)(n - azero) * x; }
            else ans += y;
            dec(a);
        }
    }
    static void dec(int[] a)
    {
        for (int i = 0; i < n; i++)
        {
            if (a[i] > 1) a[i]--;
            else if (a[i] == 1) { a[i] = 0; azero++; }
        }
    }
    static bool check(int[] a)
    {
        var b1 = (long)(n - azero) * x;
        return b1 <= y;
    }
}