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

Ex Input:
Sentence: 'children with scissors and construction paper in a school classroom'. Find frequency of the letter 'c'

Ex Output:
6


Ex Input:
Sentence: 'a couple of men sitting next to each other under an umbrella'. Find frequency of the letter 'n'

Ex Output:
5


Ex Input:
Sentence: 'boat oar held up out the water to show it's rust'. Find frequency of the letter 'o'

Ex Output:

5