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

Ex Input:
Sentence: 'a bus is driving on the street behind some cars'. Find frequency of the letter 'a'

Ex Output:
2


Ex Input:
Sentence: 'a burning wood stove has a tea pot sitting on top of it and is full of wood'. Find frequency of the letter 'a'

Ex Output:
5


Ex Input:
Sentence: 'a person standing in front of a table putting something in a blender'. Find frequency of the letter 'i'

Ex Output:

5