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

Ex Input:
Sentence: 'a bird outside standing on a table looking up'. Find frequency of the letter 'b'

Ex Output:
2


Ex Input:
Sentence: 'the snowboarder wearing a dark helmet sprays snow into the air'. Find frequency of the letter 'w'

Ex Output:
3


Ex Input:
Sentence: 'a double decker bus parked by a sidewalk'. Find frequency of the letter 'k'

Ex Output:

3