def ceildiv(a: int, b: int) -> int:
    return (a + b - 1) // b


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


def f():
    xs = sorted([ceildiv(a-1, K) for a in A])

    res = 0
    while len(xs) > 0:
        # ベホイミのコスト
        c1 = X * len(xs)
        # ベホマラーのコスト
        c2 = Y
        cost = min(c1, c2)
        ys = []
        t = xs[0]
        res += cost * t
        for x in xs:
            y = x - t
            if y > 0:
                ys.append(y)

        xs = ys

    return res


ans = f()
print(ans)







    # ベホイミ