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: 'a bird on a tree is flapping its wings'. Find frequency of the letter 'o'

Ex Output:
1


Ex Input:
Sentence: 'a messy desk is shown with outdated electronics'. Find frequency of the letter 'd'

Ex Output:

3