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

Ex Input:
Sentence: 'a man flying through the air on top of a skateboard'. Find frequency of the letter 'h'

Ex Output:
3


Ex Input:
Sentence: 'a jet flying through the clear blue sky'. Find frequency of the letter 'g'

Ex Output:
2


Ex Input:
Sentence: 'a sign posted outside of a store front window'. Find frequency of the letter 'd'

Ex Output:

3