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: 'a tv in a glass mirror in the bathroom'. Find frequency of the letter 'h'

Ex Output:
2


Ex Input:
Sentence: 'a person on a surfboard on rapids in a river'. Find frequency of the letter 'd'

Ex Output:

2