A12780 | 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.