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

Ex Input:
Sentence: 'a small dog sits in the rear window of a car'. Find frequency of the letter 'm'

Ex Output:
1


Ex Input:
Sentence: 'a man riding a skateboard up the side of a ramp'. Find frequency of the letter 'u'

Ex Output:
1


Ex Input:
Sentence: 'a bright red london double decked bus waiting at curbside'. Find frequency of the letter 't'

Ex Output:

3