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: 'a group of giraffes walk together by a hill'. Find frequency of the letter 'b'

Ex Output:
1


Ex Input:
Sentence: 'a woman is hitting a tennis ball with a racket'. Find frequency of the letter 'i'

Ex Output:

5