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

Ex Input:
Sentence: 'a sheep in a field in front of other sheep'. Find frequency of the letter 'f'

Ex Output:
3


Ex Input:
Sentence: 'a bunch of fruit sitting in a bowl, its overflowing'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'a picnic bench on the shore of a lake with mountains in the background'. Find frequency of the letter 's'

Ex Output:

2