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

Ex Input:
Sentence: 'man sitting on the side of a van playing the guitar'. Find frequency of the letter 'm'

Ex Output:
1

Ex Input:
Sentence: 'a toilet of some sort near a sink of some sort'. Find frequency of the letter 'o'

Ex Output:
7

Ex Input:
Sentence: 'many people sitting under umbrellas on a sunny beach'. Find frequency of the letter 'n'

Ex Output:
6