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

Input: Consider Input: Sentence: 'a photo of a toilet which is not clean'. Find frequency of the letter 'w'

Output: 1

Input: Consider Input: Sentence: 'a person on a skateboard going down a ramp'. Find frequency of the letter 'n'

Output: 4

Input: Consider Input: Sentence: 'a man that is sitting down laughing at a girl'. Find frequency of the letter 't'
Output: 5