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

Ex Input:
Sentence: 'a person standing operating a cell phone in a room'. Find frequency of the letter 'n'

Ex Output:
6


Ex Input:
Sentence: 'an image of a street sign with a corner restaurant'. Find frequency of the letter 'u'

Ex Output:
1


Ex Input:
Sentence: 'a train sits on a railroad track as a metal awning covers it'. Find frequency of the letter 'l'

Ex Output:

2