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 girls are hanging out at a restaurant'. Find frequency of the letter 'l'

Ex Output:
2


Ex Input:
Sentence: 'a white toilet sitting next to a bathroom sink'. Find frequency of the letter 'b'

Ex Output:
1


Ex Input:
Sentence: 'a photo of a mirror with a cats tail in the reflection'. Find frequency of the letter 'e'

Ex Output:

3