CF1213C Book Reading

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.

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.

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