N, K, X, Y = map(int, input().split())
A = list(map(int, input().split()))
A = [ (a-2+K) // K for a in A ]
A.sort()

S = [0] * (N+1)
for i in range(N-1, -1, -1):
  S[i] = S[i+1] + A[i]

ans = S[0] * X
for i in range(N):
  ans = min(ans, A[i] * Y + (S[i] - (N-i)*A[i]) * X)
print(ans)