N,K,X,Y=map(int,input().split())
a=list(map(int,input().split()))
import math
A=[]
for i in range(N):
    A.append((a[i]-1)//K)
    if (a[i]-1)%K!=0:
        A[-1]+=1
#print(A)
M=int(Y/X)
A.sort(reverse=True)
if M>N-1:
    print(sum(A)*X)
else:
    ans=A[M]
    ANS=Y*ans
    #print(ANS)
    for i in range(N):
        A[i]=max(0,A[i]-ans)
    ANS+=X*sum(A)
    print(ANS)