import sys
import pypyjit
import itertools
import heapq
import math
from collections import deque, defaultdict
import bisect

input = sys.stdin.readline
sys.setrecursionlimit(10 ** 6)
pypyjit.set_param('max_unroll_recursion=-1')


def index_lt(a, x):
    'return largest index s.t. A[i] < x or -1 if it does not exist'
    return bisect.bisect_left(a, x) - 1


def index_le(a, x):
    'return largest index s.t. A[i] <= x or -1 if it does not exist'
    return bisect.bisect_right(a, x) - 1


def index_gt(a, x):
    'return smallest index s.t. A[i] > x or len(a) if it does not exist'
    return bisect.bisect_right(a, x)


def index_ge(a, x):
    'return smallest index s.t. A[i] >= x or len(a) if it does not exist'
    return bisect.bisect_left(a, x)


N, K, X, Y = map(int, input().split())
A = list(map(lambda x: int(x) - 1, input().split()))

B = [-(-a // K) for a in A]
l = -1
r = max(B) + 1

while r - l > 1:
    c = (l + r) // 2
    rest = 0
    for b in B:
        if b > c:
            rest += 1
    if rest * X < Y:
        r = c
    else:
        l = c
ans = Y * r
for b in B:
    ans += X * max(b - r, 0)
print(ans)