N, K, X, Y = map(int, input().split()) A = list(map(int, input().split())) B = [((a - 1) + K - 1) // K for a in A] B.sort(reverse=True) if Y <= X: print(Y * B[0]) exit() t = (Y + (X - 1)) // 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)))