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

Ex Input:
Sentence: 'a silver train crossing the road on tracks'. 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: 'people and their motor scooters waiting on a city corner'. Find frequency of the letter 'e'

Ex Output:

5