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

Ex Input:
Sentence: 'a baby calf has a tag on its right ear'. Find frequency of the letter 'n'

Ex Output:
1


Ex Input:
Sentence: 'two men with colorful ties are posing for a picture'. Find frequency of the letter 'r'

Ex Output:
4


Ex Input:
Sentence: 'a yellow and white train traveling down train tracks'. Find frequency of the letter 'r'

Ex Output:

4