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

Ex Input:
Sentence: 'a couple of buildings that has a bus out front'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'a sheep in a field in front of other sheep'. Find frequency of the letter 'f'

Ex Output:
3


Ex Input:
Sentence: 'a small girl looks as an adult points with an umbrella'. Find frequency of the letter 'u'

Ex Output:

2