n,k,x,y = map(int, input().split())
a = list(map(int, input().split()))
num = [(a[i]+k-2)//k for i in range(n)]
num.sort()
s = [0] * (n+1)
for i in range(n):
    s[i+1] = num[i] + s[i]

ans = x*s[n]
ycnt = 0
for i in range(n):
    ycnt += max(0, num[i] - ycnt)
    ans = min(ans, y*ycnt + x*(s[n] - s[i] - ycnt*(n-i)))
print(ans)