Talented Chef这道题中有一点细节不是很懂。

Talented Chef这道题中有一点细节不是很懂。
As we all know, Coach Gao is a talented chef, because he is able to
cook M dishes in the same time. Tonight he is going to have a hearty
dinner with his girlfriend at his home. Of course, Coach Gao is going
to cook all dishes himself, in order to show off his genius cooking skill to his
girlfriend.
To make full use of his genius in cooking, Coach Gao decides to
prepare N dishes for the dinner. The i-th dish contains
Ai steps. The steps of a dish should be finished
sequentially. In each minute of the cooking, Coach Gao can choose at
most M different dishes and finish one step for each dish chosen.
Coach Gao wants to know the least time he needs to prepare the
dinner.
Input
There are multiple test cases. The first line of input contains an integer
T indicating the number of test cases. For each test case:
The first line contains two integers N and M (1