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

Ex Input:
Sentence: 'two boys are doing skateboard jumps in the street'. Find frequency of the letter 's'

Ex Output:
4

Ex Input:
Sentence: 'a doll with huge eyes and black hair with blunt bangs holds a red umbrella'. Find frequency of the letter 'e'

Ex Output:
5

Ex Input:
Sentence: 'a well browned baguette with a hot dog baked inside'. Find frequency of the letter 'i'

Ex Output:
3