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

Ex Input:
Sentence: 'a white police vehicle parked on a paved street'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a herd of giraffes in tall african grass'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'a man in a beige t-shirt holds up a whisk and a remote'. Find frequency of the letter 's'

Ex Output:

3