In this task, you need to count the number of times the given letter appears in the given sentence.

Input: Consider Input: Sentence: 'a double-decker bus covered in children's illustrations driving next to a van'. Find frequency of the letter 'a'

Output: 4


Input: Consider Input: Sentence: 'two men are playing a video game as another sits watching'. Find frequency of the letter 'a'

Output: 7


Input: Consider Input: Sentence: 'a small dog sitting on a stool next to his owner'. Find frequency of the letter 'n'


Output: 4