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

Ex Input:
Sentence: 'a man in costume talking on a cell phone'. Find frequency of the letter 'm'

Ex Output:
2


Ex Input:
Sentence: 'two people are riding on canoes down a river'. Find frequency of the letter 'e'

Ex Output:
5


Ex Input:
Sentence: 'four donkeys are carrying baskets by the water'. Find frequency of the letter 'e'

Ex Output:

5