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

Ex Input:
Sentence: 'a young boy standing in front of a counter with dougnuts'. Find frequency of the letter 'o'

Ex Output:
6


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

Ex Output:
2


Ex Input:
Sentence: 'a computer with a musical keyboard attached in a music store'. Find frequency of the letter 'n'

Ex Output:

1