import sys

sys.setrecursionlimit(200005)
int1 = lambda x: int(x)-1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.buffer.readline())
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def LI1(): return list(map(int1, sys.stdin.buffer.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def BI(): return sys.stdin.buffer.readline().rstrip()
def SI(): return sys.stdin.buffer.readline().rstrip().decode()
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
dij = [(0, 1), (1, 0), (1, 1), (1, -1)]
inf = 10**16
# md = 998244353
md = 10**9+7

n, k, x, y = LI()
aa = LI()
aa.sort(reverse=True)
aa = [(a+k-2)//k for a in aa]

def cost(m):
    res = m*y
    for a in aa:
        if a-m <= 0: break
        res += (a-m)*x
    return res

l, r = 0, max(aa)+1
while l+1 < r:
    m = (l+r)//2
    # print(l,r,m,cost(m-1),cost(m))
    if cost(m-1) > cost(m): l = m
    else: r = m

print(cost(l))