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

Ex Input:
Sentence: 'statues of 2 zebras and 1 giraffe in a doorway'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'young boy flying kite in large field at outdoor event'. Find frequency of the letter 'y'

Ex Output:
3


Ex Input:
Sentence: 'a vase and flower with a plate sit with a lawn set'. Find frequency of the letter 'a'

Ex Output:

7