n,k,x,y = map(int,input().split())
a = [int(i)-1 for i in input().split()]

low = 0
high = (k-1+max(a))//k

def f(num):
    val = num*y
    for i in range(n):
        tmp = (max(0,a[i]-num*k)+k-1)//k
        val += tmp*x
    return val
#print(low,high)
#exit()
cnt = 0
while low+1 < high:
    c1 = int((low*2+high)/3)
    c2 = int((low+high*2)/3)
    
    if f(c1) > f(c2):
        if low == c1:
            low += 1
        else:
            low = c1
    else:
        if high == c2:
            high -= 1
        else:
            high = c2

ans = min(f(high),f(low))
print(ans)