using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static int[][] NArr(long n) => Enumerable.Repeat(0, (int)n).Select(_ => NList).ToArray();
    static int[] NMi => ReadLine().Split().Select(c => int.Parse(c) - 1).ToArray();
    static int[][] NMap(int n) => Enumerable.Repeat(0, n).Select(_ => NMi).ToArray();
    static string[] SList(long n) => Enumerable.Repeat(0, (int)n).Select(_ => ReadLine()).ToArray();
    static long[] LList(long n) => Enumerable.Repeat(0, (int)n).Select(_ => long.Parse(ReadLine())).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (n, k, x, y) = (c[0], c[1], c[2], c[3]);
        var a = NList;
        WriteLine(Heal(n, k, x, y, a));
    }
    static long Heal(int n, int k, int x, int y, int[] a)
    {
        var count = new int[n];
        for (var i = 0; i < n; ++i)
        {
            count[i] = (a[i] - 1 + k - 1) / k;
        }
        Array.Sort(count);
        var cum = new long[n + 1];
        for (var i = 0; i < n; ++i) cum[i + 1] = cum[i] + count[i];
        var allsingle = cum[^1] * x;
        if (allsingle / x != cum[^1]) allsingle = long.MaxValue;
        var ans = Math.Min(allsingle, (long)count[^1] * y);
        for (var i = 0; i < n; ++i)
        {
            ans = Math.Min(ans, (long)count[i] * y + (cum[^1] - cum[i + 1] - (long)count[i] * (n - i - 1)) * x);
        }
        return ans;
    }
}