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

Ex Input:
Sentence: 'a woman walking with a child that is in a wheelchair'. Find frequency of the letter 'k'

Ex Output:
1


Ex Input:
Sentence: 'a young boy bouncing a tennis ball on a tennis racquet'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'three cows are eating grass on the hillside'. Find frequency of the letter 'w'

Ex Output:

1