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

Input: Consider Input: Sentence: 'a giraffe shares a habitat with a zebra, an ostrich, and an okapi'. Find frequency of the letter 'e'

Output: 3

Input: Consider Input: Sentence: 'a black cat laying down on a bed'. Find frequency of the letter 'y'

Output: 1

Input: Consider Input: Sentence: 'a man flying through the air while riding a snowboard'. Find frequency of the letter 'n'
Output: 4