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

Ex Input:
Sentence: 'men are riding on motorcycles with a man riding in their carriers'. Find frequency of the letter 'r'

Ex Output:
8


Ex Input:
Sentence: 'a number of small boats on a beach near an umbrella'. Find frequency of the letter 's'

Ex Output:
2


Ex Input:
Sentence: 'a giraffe standing next to a stone wall'. Find frequency of the letter 'n'

Ex Output:

4