n,k,x,y = map(int, input().split())
a = list(map(int, input().split()))
newa=[]

def ceil(a,b):
    return ((a - 1) // b) + 1

for tmp in a:
    if tmp==1:
        continue
    newa.append(ceil(tmp-1,k))

newa.sort()

all_cnt=0
single_cnt=0
nokori=len(newa)

for num in newa:
    need = num - all_cnt
    if nokori*x >= y:
        all_cnt+=need
        nokori-=1
    else:
        single_cnt+=need

print(all_cnt*y + single_cnt*x)