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

Ex Input:
Sentence: 'a red and white train passing a train station'. Find frequency of the letter 'a'

Ex Output:
7


Ex Input:
Sentence: 'a long row of tables displaying lots of fruit'. Find frequency of the letter 'o'

Ex Output:
5


Ex Input:
Sentence: 'a woman petting brown horses on top of a field'. Find frequency of the letter 'o'

Ex Output:

6