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

Ex Input:
Sentence: 'a cat sprawls out and sleeps on its back on a lounge chair with an acorn theme'. Find frequency of the letter 'r'

Ex Output:
3


Ex Input:
Sentence: 'several zebras  and a giraffe in an enclosure'. Find frequency of the letter 's'

Ex Output:
3


Ex Input:
Sentence: 'a large black steer walking away with a small stuffed teddy bear in a pile of brush'. Find frequency of the letter 'u'

Ex Output:

2