n,k,x,y=map(int,input().split())
a=list(map(int,input().split()));a.sort()
ans=0;c=0;f=0
for i in range(n):
	a[i]-=1
	ans+=(a[i]+k-1)//k*x
c=ans;t=0
for i in range(n):
    e=a[i]//k
    if e>f:
        c-=(n-i)*(e-f)*x
        t+=(e-f)*y
        f=e
        ans=min(ans,c+t)
    e+=1
    if a[i]%k and c>=x*(n-i) and e>f:
        c-=(n-i)*x
        t+=y;f=e
    ans=min(ans,c+t)
print(ans)