Grading Exams

Ms. Garrette needs help grading her multiple choice exams. To prevent cheating, she gave each student an individualized exam. Given an answer key and one student's responses, count how many of that student's answers are wrong.

The first line contains the number of test cases.

Each test case begins with an integer $L$ ($0 < L \le 100$), the number of questions on the exam. The next line contains the answer key, where the correct answer to each question is a single letter a, b, c, or d. The line after that contains the student's responses in the same format.

For each test case, print one line in the form Case x: y. Here x is the case number and y is the number of student responses that did not match the answer key.