import sys
import math
import itertools
import bisect
from copy import copy
from collections import deque,Counter
from decimal import Decimal
def s(): return input()
def i(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def L(): return list(input().split())
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
mod = 10**9+7

N,K,X,Y = I()
A = l()
A.sort(reverse=True)
A = [math.ceil((A[i]-1)/K) for i in range(N)]
B = math.ceil(X/Y)
if X > Y:
    print(max(A))
    exit()
if X*N < Y:
    B = N+1
C = A[0:B]
if A[B:]:
    D = max(A[B:])
else:
    D = 0
ans = 0
for c in C:
    ans += X*(c-D)
ans += D*Y
print(ans)