n, k, x, y = map(int, input().split())
alst = list(map(int, input().split()))
cnt = [(a - 2) // k + 1 for a in alst]
cnt.sort(reverse = True)
x_s = min(y // x - 1, n - 1)
ans = 0
y_cnt = 0
if x_s != n - 1:
    y_cnt = cnt[x_s + 1]
    ans = y * y_cnt
for i in range(x_s + 1):
    ans += x * (cnt[i] - y_cnt)
print(ans)