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

Ex Input:
Sentence: 'a young man with glasses on is taking a big bite'. Find frequency of the letter 's'

Ex Output:
4

Ex Input:
Sentence: 'two people holding their skies in a snowy resort'. Find frequency of the letter 'n'

Ex Output:
3

Ex Input:
Sentence: 'the miniature, elaborate exhibit depicts an ancient boating scene'. Find frequency of the letter 'n'

Ex Output:
6