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

Ex Input:
Sentence: 'a man walking a large elephant down a dirt road'. Find frequency of the letter 'g'

Ex Output:
2


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 big screen tv and a brown chair and blue table'. Find frequency of the letter 'a'

Ex Output:

6