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

Ex Input:
Sentence: 'a girl playing with a frisbee while people watch'. Find frequency of the letter 'e'

Ex Output:
5


Ex Input:
Sentence: 'older man getting ready to swing his bat at a ball on a stand in front of a group of viewers'. Find frequency of the letter 'n'

Ex Output:
7


Ex Input:
Sentence: 'a tiny bird sits on a car's mirror'. Find frequency of the letter 'y'

Ex Output:

1