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

Ex Input:
Sentence: 'man in red shirt with black suitcase standing outside of building'. Find frequency of the letter 'i'

Ex Output:
8


Ex Input:
Sentence: 'a railroad train pulling up to the train platform'. Find frequency of the letter 'o'

Ex Output:
3


Ex Input:
Sentence: 'a wooden side table holding a potted plant'. Find frequency of the letter 't'

Ex Output:

4