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]

ans = R[0]*X
for i in range(0,N):
    now = B[i]*Y+(R[i+1]-(N-1-i)*B[i])*X
    ans = min(ans,now)
print(ans)