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 metallic stove top oven inside of a wooden kitchen'. Find frequency of the letter 'v'

Ex Output:
2


Ex Input:
Sentence: 'a man on a motor bike on the street'. Find frequency of the letter 'a'

Ex Output:

3