n, k, x, y = map(int, input().split())
A = list(map(int, input().split()))

B = [0 for _ in range(n)]
for i in range(n):
    B[i] = (A[i] - 1 + k - 1) // k
B.sort(reverse=True)

if y <= x:
    print(y * B[0])
    exit()
t = (y + x - 1) // x - 1
if t < n:
    print(y * B[t] + x * sum(B[i] - B[t] for i in range(t)))
else:
    print(x * sum(B))