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

Ex Input:
Sentence: 'a man working on a small laptop on a wooden table'. Find frequency of the letter 'l'

Ex Output:
4


Ex Input:
Sentence: 'a person holding onto a pink kite at the beach'. Find frequency of the letter 'n'

Ex Output:
4


Ex Input:
Sentence: 'an older man walking with a cane crossing the street'. Find frequency of the letter 'a'

Ex Output:

5