def main():
    A, B, C, D, E = map(int, input().split())
    people = B - C
    candy = A * people

    candy_price = D
    money_needed = 0
    for idx in range(1, candy+1):
        if idx % 10 == 0 and E <= candy_price:
            candy_price -= E

        money_needed += candy_price

    print(money_needed)


if __name__ == "__main__":
    main()