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 wearing snowboards sitting on a snowy slope'. Find frequency of the letter 's'

Output: 5

Input: Consider Input: Sentence: 'a piece of meat covered in ketchup next to a hamburger on a green plate'. Find frequency of the letter 'g'

Output: 2

Input: Consider Input: Sentence: 'a chubby cat sits under a parked car in the shade'. Find frequency of the letter 'a'
Output: 6