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

Input: Consider Input: Sentence: 'a white toilet sitting next to a toilet paper roller'. Find frequency of the letter 'o'

Output: 4

Input: Consider Input: Sentence: 'a guy surfs a wave with his surfboard'. Find frequency of the letter 's'

Output: 4

Input: Consider Input: Sentence: 'four road signs giving different information by a brick building'. Find frequency of the letter 'b'
Output: 3