import sys

sys.setrecursionlimit(10 ** 8)

input = sys.stdin.readline


def main():
    N, K, X, Y = [int(x) for x in input().split()]
    A = [int(x) for x in input().split()]

    A.sort()

    cnt = N - A.count(1)
    if cnt == 0:
        print(0)
        return

    m = Y // X
    m = N - 1 - m
    ans = 0
    if m < 0:
        for i in range(N):
            ans += -(-(A[i] - 1) // K) * X
    else:
        ans = -(-(A[min(N - 1, m)] - 1) // K) * Y
        xx = -(-(A[min(N - 1, m)] - 1) // K)
        for i in range(m + 1, N):
            ans += -(-(A[i] - (1 + xx * K)) // K) * X

    print(ans)

if __name__ == '__main__':
    main()