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

Ex Input:
Sentence: 'a group of people standing around a table filled with assorted electronic devices'. Find frequency of the letter 'w'

Ex Output:
1


Ex Input:
Sentence: 'a person that is looking out his window'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a blue and white bus parked on the side of the road'. Find frequency of the letter 'r'

Ex Output:

2