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

Input: Consider Input: Sentence: 'a car accident has slowed traffic as a clean up crew works'. Find frequency of the letter 'f'

Output: 2

Input: Consider Input: Sentence: 'a parking meter painted green with a sign that describes it as not a parking meter'. Find frequency of the letter 's'

Output: 4

Input: Consider Input: Sentence: 'a cart of luggage on a asphalt runway'. Find frequency of the letter 'n'
Output: 2