Compare those strings ~ Multiplex Coder

Chef has two strings

$A$ and $B$ consisting of lowercase alphabets, each of length $N$ . Help Chef in finding the number of indices $i$ $(1 \leq i \leq N)$ such that $A [i \dots N] < B [i \dots N]$ .

$S [i \dots N]$ denotes the suffix of string $S$ starting at index $i$ , i.e. $S_{i} S_{i + 1}$ $\dots$ $S_{N}$ .
String $S <$ String $T$ denotes that $S$ is lexicographically smaller than $T$ . If two strings $S$ and $T$ have the same length $N$ , we say that $S$ is lexicographically smaller than $T$ if there exists an index $i (1 \leq i \leq N)$ such that $S_{1} = T_{1},$ $S_{2} = T_{2}, \dots, S_{i - 1} = T_{i - 1}$ and $S_{i} < T_{i}$ . For example, " $a b c$ " is lexicographically smaller than " $a c d$ ", " $a b e$ ", but not smaller than " $a b c$ ", " $a a c$ ".

Input Format

The first line contains $T$ denoting the number of test cases. Then the test cases follow.
The first line of each test case contains $N$ , denoting the length of the strings $A$ and $B$ .
The second line of each test case contains the string $A$ .
The third line of each test case contains the string $B$ .

Output Format

For each test case, print a single line containing one integer - the number of indices $i$ such that $A [i \dots N] < B [i \dots N]$ .

Constraints

$1 \leq T \leq 10^{5}$
$1 \leq N \leq 10^{6}$
The sum of $N$ over all test cases does not exceed $10^{6}$

Sample Input 1

2
2
ab
bb
3
aaa
aab

Sample Output 1

1
3

Explanation

Test Case $1$ :

For $i = 1$ , $A [1 \dots 2] =$ " $a b$ ", $B [1 \dots 2] =$ " $b b$ " and lexicographically, " $a b$ " $<$ " $b b$ ".
For $i = 2$ , $A [2 \dots 2] =$ " $b$ ", $B [2 \dots 2] =$ " $b$ " and lexicographically, " $b$ " $=$ " $b$ ".

Test Case $2$ : For each $i \in {1, 2, 3}$ , $A [i \dots 3] < B [i \dots 3]$ .

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