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

Input: Consider Input: Sentence: 'a surfer wipes out on a huge wave'. Find frequency of the letter 'a'

Output: 3

Input: Consider Input: Sentence: 'a train is sitting at a train station'. Find frequency of the letter 'r'

Output: 2

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