N, K, X, Y = map(int, input().split())
A = tuple(map(int, input().split()))

ceil = lambda a, b: (a + b - 1) // b

An = sorted([ceil(a - 1, K) for a in A])
c = Y // X
if c == 0:
    print(N)
elif c > N:
    print(sum(An) * X)
else:
    print(An[N - c - 1] * Y + (sum(An[N - c:]) - An[N - c - 1] * c) * X)