import math

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

B=[(a-1+K-1)//K for a in Ax]
B.sort(reverse=True)
if Y <= X:
    print(Y*B[0])
    exit()

t = math.ceil(Y/X)-1
if t<N:
    print(Y * B[t] + X * sum(B[i] - B[t] for i in range(t)))
else:
    print(X * sum(B[i] for i in range(N)))