n,k,x,y = map(int,input().split())
A = list(map(int,input().split()))
l = 0
r = 10**20

def calc(m):
    count = 0
    for a in A:
        if a-1 <= m*k:
            continue
        count += (a-1-m*k+(k-1))//k*x
    return count + y*m


while r > l+2:
    c1 = (l*2+r)//3
    c2 = (l+r*2)//3
    if calc(c1) <= calc(c2):
        r = c2
    else:
        l = c1

ans = 10**20
for i in range(l,r+2):
    ans = min(ans,calc(i))
print(ans)