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

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

Ex Output:
3


Ex Input:
Sentence: 'a person is holding a chocolate doughnut with rainbow sprinkles'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'a back view of a man swinging a baseball bat'. Find frequency of the letter 's'

Ex Output:

2