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

Ex Input:
Sentence: 'a woman cross country skiing in a competition'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'a glass bowl of raw broccoli, a ceramic bowl of raw green chili peppers, and steel bowl of raw daikon'. Find frequency of the letter 'a'

Ex Output:
9


Ex Input:
Sentence: 'a male and female couple a boat and water'. Find frequency of the letter 'a'

Ex Output:

8