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

Ex Input:
Sentence: 'a man with glasses adjusting his tie in a mirror'. Find frequency of the letter 's'

Ex Output:
5


Ex Input:
Sentence: 'a herd of zebra standing on top  of a grass covered field'. Find frequency of the letter 'e'

Ex Output:
5


Ex Input:
Sentence: 'a small child eating a cake with its hands'. Find frequency of the letter 's'

Ex Output:

3