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

Input: Consider Input: Sentence: 'two people under an umbrella while walking down a sidewalk'. Find frequency of the letter 'i'

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 half eaten bunt cake sits on a white plate'. Find frequency of the letter 'a'
Output: 6