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

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

Ex Output:
1


Ex Input:
Sentence: 'a person is riding in a cart pulled by a horse'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a scooter siting on the side of a wall overlooking a water way and a sail boat'. Find frequency of the letter 'i'

Ex Output:

5