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

Input: Consider Input: Sentence: 'a passenger bus that is driving down the street'. Find frequency of the letter 'r'

Output: 3


Input: Consider Input: Sentence: 'a person working at an airport, outside of an airplane'. Find frequency of the letter 'r'

Output: 5


Input: Consider Input: Sentence: 'a chickadee sitting on a tree branch in the winter'. Find frequency of the letter 'a'


Output: 4