# 想定解法でやってみる

N, K, X, Y = map(int, input().split())
A = list(map(int, input().split()))

AK = [0]
for a in A:
    calc = (a-1+K-1)//K
    AK.append(calc)
AK.sort()
    
#print(AK)

if sum(AK) == 0:
    print(0)
    exit()

ans = 0
y = 0
for i in range(N):
    remaining = N-i
    if X*remaining > Y:
        y = i+1
    else:
        ans += (AK[i+1]-AK[y])*X
ans += AK[y]*Y
print(ans)