num_candy,num_invite,num_reject,price,discount = map(int,input().split())
num2buy = num_candy * (num_invite - num_reject)

def mark_down():
    global price, discount
    price -= discount if price >= discount else 0

total = 0
for i in range(num2buy):
    if (i + 1) % 10 == 0:
        mark_down()
    total += price
print(total)