N,K,X,Y = map(int,input().split())
A = list(map(int,input().split()))
AK = [0]*(N+1)
for i in range(N):
    AK[i] = -(-(A[i]-1)//K)
AK.sort()
SAK = sum(AK)
ans = SAK*X
behoi = SAK
for i in range(N):
    behoi -= (AK[i+1]-AK[i])*(N-i)
    behoma = AK[i+1] 
    ans = min(ans,behoi*X+behoma*Y)

print(ans)