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

Ex Input:
Sentence: 'a group of tennis players on a tennis court'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'a train on a train track going through a bunch of trees'. Find frequency of the letter 'u'

Ex Output:
2


Ex Input:
Sentence: 'a laptop computer with pictures of giraffes on the homescreen'. Find frequency of the letter 'o'

Ex Output:

5