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

Ex Input:
Sentence: 'a small wrinkley dog wearing a bow tie'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'two people holding their skies in a snowy resort'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a plate full of lettuce, perhaps a salad'. Find frequency of the letter 'r'

Ex Output:

1