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 man standing on a tennis court holding a racquet'. Find frequency of the letter 's'

Ex Output:
2


Ex Input:
Sentence: 'a airplane view of a big factory some people and cars'. Find frequency of the letter 'f'

Ex Output:

2