先完成以下 6 道贪心练习题（CF rating 1800）

• CF1870D Prefix Purchase 1800
• CF1861D Sorting By Multiplication 1800
• CF1859D Andrey and Escape from Capygrad 1800
• CF1841C Ranom Numbers 1800
• CF1748C Zero-Sum Prefixes 1600
• CF1707A Doremy's IQ 1600