n,k,x,y = map(int,input().split())
a = [int(i) for i in input().split()]
ans = 0
for i in range(n):
    ans += ((a[i]-1+k-1)//k)*x
a = sorted(a)
for i in range(n):
    a[i] = a[i]-1
sum = []
for i in range(n+1):
    sum.append(0)

for i in range(n):
    sum[n-i-1] = sum[n-i] + ((a[n-i-1]+k-1)//k)*x

for i in range(n):
    cnt = a[i]//k
    if(a[i]%k!=0): cnt += 1
    ret = sum[i+1] + cnt*y
    ret -= x*cnt*(n-i-1)
    if(ans > ret): ans=ret
print(ans)