using System.Linq;
using System;

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var n = int.Parse(line[0]);
        var k = int.Parse(line[1]);
        var x = int.Parse(line[2]);
        var y = int.Parse(line[3]);
        var a = new long[n];
        line = Console.ReadLine().Trim().Split(' ');
        for (int i = 0; i < n; i++)
            a[i] = (int.Parse(line[i]) + k - 2) / k;
        var ans = getAns(n, x, y, a);
        Console.WriteLine(ans);
    }
    static long getAns(int n, int x, int y, long[] a)
    {
        Array.Sort(a);
        var nz = y / x;
        if (nz == 0) return a.Max() * y;
        if (nz >= n) return a.Sum() * x;
        var p = n - nz - 1;
        var ans = a[p] * y;
        var tsum = 0L;
        for (int i = p + 1; i < n; i++) tsum += a[i];
        tsum -= nz * a[p];
        ans += tsum * x;
        return ans;
    }
}