from math import ceil


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

    A.sort(reverse=True)

    rate = Y / X

    if ceil(rate) > len(A):
        all_num = 0
    else:
        all_num = ceil((A[min(ceil(rate), len(A))-1] - 1) / K)

    A_rest = list(filter(lambda num: num > 0, map(
        lambda num: num - all_num*K, A)))
    partial_num = sum(map(lambda num: ceil((num - 1)/K), A_rest))
    print(all_num * Y + partial_num * X)


if __name__ == "__main__":
    main()