import sys
input = sys.stdin.readline

N,K,X,Y=map(int,input().split())
A=list(map(int,input().split()))

R=[(a-1+K-1)//K for a in A]
import heapq
heapq.heapify(R)

ANS=0
common=0

#print(R)

while R:
    #print(ANS,R)
    while R and R[0]<=common:
        heapq.heappop(R)

    if len(R)*X>Y:
        ANS+=(R[0]-common)*Y
        common+=R[0]-common
    else:
        for t in R:
            ANS+=max(0,t-common)*X
        break
print(ANS)