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: 'an empty clean kitchen with island, marble countertops , stove and cabinetry'. Find frequency of the letter 'l'

Ex Output:
3


Ex Input:
Sentence: 'a double-decker red bus on a london street'. Find frequency of the letter 's'

Ex Output:

2