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

Ex Input:
Sentence: 'group of snowboarders on a snowy trail overlooking a mountain'. Find frequency of the letter 'r'

Ex Output:
5


Ex Input:
Sentence: 'a log in the water with three birds perched on it'. Find frequency of the letter 'r'

Ex Output:
4


Ex Input:
Sentence: 'a blonde haired woman pushing a bicycle and talking on a cell phone'. Find frequency of the letter 'o'

Ex Output:

4