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: 'an old woman is holding her cat in front of a camera'. Find frequency of the letter 'r'

Ex Output:
3


Ex Input:
Sentence: 'a young girl is talking on her cell phone'. Find frequency of the letter 'r'

Ex Output:

2