Lena economical girl Moscow so dad ask buy food trip country go good store PriceFixed here rule store the store infinite number item product all product price 2 ruble item for product discount experience buyer buy b_i item product type necessarily type future purchase ith product 50 discount buy item ith product 1 ruble Lena need buy n product purchase a_i item ith product help Lena calculate minimum money need spend optimally choose order purchase note want buy item product need