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

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: 'the receipts from a meal at a restaurant are for  a sandwich, chili, and apple'. Find frequency of the letter 'u'

Output: 1


Input: Consider Input: Sentence: 'a train at night shining it's lights going by a sign'. Find frequency of the letter 'n'


Output: 6