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

Input: Consider Input: Sentence: 'a police officer who is riding on a horse'. Find frequency of the letter 'p'

Output: 1

Input: Consider Input: Sentence: 'a cat sprawls out and sleeps on its back on a lounge chair with an acorn theme'. Find frequency of the letter 'r'

Output: 3

Input: Consider Input: Sentence: 'a woman on her bed very sad looking'. Find frequency of the letter 'y'
Output: 1