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

Ex Input:
Sentence: 'a dog on a couch near many pillows'. Find frequency of the letter 'p'

Ex Output:
1

Ex Input:
Sentence: 'an audience watches as a bird spreads its wings'. Find frequency of the letter 'd'

Ex Output:
3

Ex Input:
Sentence: 'a picture of a sign post for a bikelane at the corner of hancock ave'. Find frequency of the letter 'f'

Ex Output:
3