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 wedding cake with pink roses on a silver plate'. Find frequency of the letter 'a'

Output: 4

Input: Consider Input: Sentence: 'a small elephant standing up against a stone wall'. Find frequency of the letter 's'
Output: 4