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

Ex Input:
Sentence: 'a person standing operating a cell phone in a room'. Find frequency of the letter 'n'

Ex Output:
6


Ex Input:
Sentence: 'two people wearing snowboards sitting on a snowy slope'. Find frequency of the letter 's'

Ex Output:
5


Ex Input:
Sentence: 'a surfer riding a way into shore while another surfer watches from shore'. Find frequency of the letter 'g'

Ex Output:

1