Book Reading

题意翻译

题目描述： 有一本包含$n$页的书，页码编号从$1$到$n$。每当你读完一页并且页码能被m整除，你就会记下此页码的最后一位数字。例如，如果$n=15$且$m=5$，则可被$m$整除的页码为$5,10,15$。 他们的最后数字相应地为$5,0,5$，其总和为$10$。 计算你写下的所有数字的总和。 输入格式： 输入的第一行包含一个整数$q\ (1≤q≤1000)$，即查询数量。 以下$q$行每行包含两个整数$n,m\ (1\leq n,m\leq 10^{16})$。 输出格式： 对于每组查询输出你写下的数字总和。

题目描述

Polycarp is reading a book consisting of $ n $ pages numbered from $ 1 $ to $ n $ . Every time he finishes the page with the number divisible by $ m $ , he writes down the last digit of this page number. For example, if $ n=15 $ and $ m=5 $ , pages divisible by $ m $ are $ 5, 10, 15 $ . Their last digits are $ 5, 0, 5 $ correspondingly, their sum is $ 10 $ . Your task is to calculate the sum of all digits Polycarp has written down. You have to answer $ q $ independent queries.

输入输出格式

输入格式

The first line of the input contains one integer $ q $ ( $ 1 \le q \le 1000 $ ) — the number of queries. The following $ q $ lines contain queries, one per line. Each query is given as two integers $ n $ and $ m $ ( $ 1 \le n, m \le 10^{16} $ ) — the number of pages in the book and required divisor, respectively.

输出格式

For each query print the answer for it — the sum of digits written down by Polycarp.

输入输出样例

输入样例 #1

7
1 1
10 1
100 3
1024 14
998244353 1337
123 144
1234312817382646 13

输出样例 #1

1
45
153
294
3359835
0
427262129093995