import numpy as np
import math
n,k,x,y = map(int , input().split())
a = list(map(int, input().split()))
a.sort()
a = np.array(a)
ans = 0
count = 0
val = y//x
# print(val)
a-=1
while True:
    if max(a) > 0:
        if val > n:
            for i in a:
                ans += math.ceil(i/k)
                # print(i)
                # print(a)
            print(ans)
            exit()
        while val >= 0:
            while a[-val-1] > 1:
                # a -= k
                tmp = math.ceil(a[-val-1]/k)
                a -= k * tmp
                ans += y * tmp
                # print('a')
                # print(a)
            while a[-val] > 1:
                tmp = math.ceil(a[-val]/k)
                a[-val] -= k * tmp
                ans += x * tmp
                # print('b')
                # print(a)
            val -= 1
        # print(a)

    else:
        print(ans)
        exit()