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

Ex Input:
Sentence: 'a toasted sub sandwich is next to a salad'. Find frequency of the letter 'a'

Ex Output:
6


Ex Input:
Sentence: 'a bird in a tree looking up at branches'. Find frequency of the letter 'e'

Ex Output:
3


Ex Input:
Sentence: 'this is a man playing on a tennis court'. Find frequency of the letter 'o'

Ex Output:

2