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

a.sort(reverse = True)

if x > y:
    print(a[0]*y)
    exit()

k = y//x

if k < n:
    ans = y*a[k] + x*sum([a[i] - a[k] for i in range(k)])
    print(ans)
else:   
    print(sum(a)*x)