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

Ex Input:
Sentence: 'two bears swim in a blue pool of water'. Find frequency of the letter 'o'

Ex Output:
4


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 baseball player throws his arm back to make a pitch'. Find frequency of the letter 'r'

Ex Output:

3