#yuki1071
N,K,X,Y=map(int,input().split())
A=list(map(int,input().split()))
B=[0]*N
for i in range(0,N):
 B[i]=(A[i]+K-2)//K
B.sort()
R=[0]*(N+1)
for i in range(0,N):
 R[N-i-1]=R[N-i]+B[N-i-1]
res=R[0]*X
for i in range(0,N):
 t=B[i]*Y+(R[i+1]-(N-1-i)*B[i])*X
 res=min(res,t)
print(res)