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

Ex Input:
Sentence: 'a guy surfs a wave with his surfboard'. Find frequency of the letter 's'

Ex Output:
4


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: 'a man walking a large elephant down a dirt road'. Find frequency of the letter 'g'

Ex Output:

2