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

Ex Input:
Sentence: 'a big bear walks through some grass'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'two baseball players high five each other during a game'. Find frequency of the letter 'y'

Ex Output:
1


Ex Input:
Sentence: 'smoothing over the top layer of a pie'. Find frequency of the letter 'a'

Ex Output:

2