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

Ex Input:
Sentence: 'a group of people having dinner and drinking wine'. Find frequency of the letter 'r'

Ex Output:
3


Ex Input:
Sentence: 'a chair and umbrella on a sandy beach'. Find frequency of the letter 's'

Ex Output:
1


Ex Input:
Sentence: 'a white air plane flying in the air with its landing gear'. Find frequency of the letter 'g'

Ex Output:

3