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

Ex Input:
Sentence: 'three men in military suits are sitting on a bench,'. Find frequency of the letter 'a'

Ex Output:
3


Ex Input:
Sentence: 'two elephants walking on cement next to wall'. Find frequency of the letter 'n'

Ex Output:
5


Ex Input:
Sentence: 'a football player laying on the ground holding a football while another player is holding him'. Find frequency of the letter 't'

Ex Output:

4