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], reverse=True)

    res = 0
    tot = 0  # 回復合計
    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)

        t = xs[-1] - tot
        res += cost * t
        tot += t
        while xs and xs[-1] <= tot:
            xs.pop()

    return res


ans = f()
print(ans)