Book Reading

1000ms

262144K

Description:

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.

Input:

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.

Output:

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

Sample Input:

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

Sample Output:

1
45
153
294
3359835
0
427262129093995

Informação

Provedor Codeforces

Código CF1213C