The first line of the input contains a single integer $T$ ($1 \le T \le 250$), the number of test cases.
The first line of each test case contains a single integer $n$ ($1 \le n \le 10^5$), the number of columns of boards $a$ and $b$.
The next two lines contain the boards $a$ and $b$ respectively. Each board is represented by a string of length $n$ consisting of digits and dots.
The total sum of $n$ over all test cases doesn't exceed $2 \times 10^6$.