def ceil_div(x, y):
    ret = x // y
    if x % y == 0: 
        return ret
    else:
        return ret + 1;

def calc(n, k, x, y, av, ycnt):
    ret = y * ycnt
    for e in av:
        rest = e - k * ycnt
        if rest <= 0:
            continue
        ret += x * ceil_div(rest, k)
    return ret


tmp = tuple(list(map(int, input().split(' '))))
a = list(map(int, input().split(' ')))
av = [ e - 1 for e in a ]
n, k, x, y = tmp
x0 = 0
x3 = int(1e18)
f = lambda arg: calc(n, k, x, y, av, arg)
while 2 < x3 - x0:
    x1 = (2 * x0 + x3) // 3
    x2 = (x0 + 2 * x3) // 3
    f1 = f(x1)
    f2 = f(x2)
    if f1 < f2:
        x3 = x2
    else:
        x0 = x1
print(min([f(x0), f(x0+1), f(x0+2)]))