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

Ex Input:
Sentence: 'two computers and a laptop set up on a desk'. Find frequency of the letter 'r'

Ex Output:
1


Ex Input:
Sentence: 'a person is holding a chocolate doughnut with rainbow sprinkles'. Find frequency of the letter 's'

Ex Output:
4


Ex Input:
Sentence: 'a group of people walking down a rain soaked street with umbrellas'. Find frequency of the letter 'w'

Ex Output:

3