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

Ex Input:
Sentence: 'a gray elephant is in a grassy field'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'a photo of a toilet which is not clean'. Find frequency of the letter 'w'

Ex Output:
1


Ex Input:
Sentence: 'a girl is hitting a tennis ball with a racquet'. Find frequency of the letter 't'

Ex Output:

5