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()
s = sum(a)
before = 0
ans = 0

for i in range(n):
    if (s-(n-i)*(a[i] - before))*x > y*(a[i] - before):
        ans += y*(a[i] - before)
        s -= (n-i)*(a[i] - before)
        before = a[i]
    else:
        MIN = 10**10
        for g in range(a[i]-before+1):
            if MIN > (s-(n-i)*g)*x+g*y:
                MIN = (s-(n-i)*g)*x+g*y
            else:
                break
        ans += MIN
        break

print(ans)