Book Reading
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.
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.
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.
Samples
7
1 1
10 1
100 3
1024 14
998244353 1337
123 144
1234312817382646 13
1
45
153
294
3359835
0
427262129093995