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

Ex Input:
Sentence: 'two young ladies that are dancing in the room together'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a double decker transit bus parks by a blue on the side of the street in front of a brick building in the city'. Find frequency of the letter 't'

Ex Output:
9


Ex Input:
Sentence: 'a small elephant standing up against a stone wall'. Find frequency of the letter 's'

Ex Output:

4