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

Ex Input:
Sentence: 'pedestrians pass by a stop sign, some holding surfboards'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'several zebras  and a giraffe in an enclosure'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'doorway view of bathroom with a sink, toilet and shower'. Find frequency of the letter 's'

Ex Output:

2