N, K, X, Y = map(int, input().split())
A = list(map(int, input().split()))
B = list(map(lambda x: ((x - 1) + (K - 1))//K, A))
maxB = max(B)
if X > Y:
    exit(print(maxB))

# 三分探索
def f(x): # ベホマラーをx回使うときの全体コスト
    cnt = 0
    for b in B:
        if b > x:
            cnt += b - x
    return x*Y + cnt*X

left = 0
right = maxB

while right - left > 5:
    m1 = (left * 2 + right)//3
    m2 = (left + right * 2)//3

    if f(m1) > f(m2):
        # left ~ m1 間には存在しない
        left = m1
    else:
        right = m2

ans = 1e18
for i in range(left, right + 1):
    ans = min(ans, f(i))
print(ans)