N, K, X, Y = map(int, input().split())
A = list(map(int, input().split()))
A.sort()
A.append(0)
for i in range(N):
    A[i] -= 1
    A[i] = -(-A[i] // K)
B = [0] * (N + 1)
for i in reversed(range(N)):
    B[i] += B[i + 1] + A[i]
tmp = 0
ans = B[0] * X
# print(A,B)
for i in range(N):
    ans = min(ans, A[i] * Y + (B[i + 1] - A[i] * (N - i - 1)) * X)
    # print(i,A[i] * Y,B[i + 1] - A[i] * (N - i - 1))

print(ans)