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 baseball player dropping his bat and starting to run'. Find frequency of the letter 'o'

Ex Output:
2


Ex Input:
Sentence: 'the zebras are in the grassy field with the giraffes'. Find frequency of the letter 'i'

Ex Output:

4