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

Ex Input:
Sentence: 'two metal  benches on an empty train platform'. Find frequency of the letter 'n'

Ex Output:
4


Ex Input:
Sentence: 'young girl playing with refrigerator magnet while kneeling on floor'. Find frequency of the letter 'n'

Ex Output:
6


Ex Input:
Sentence: 'a male on a bicycle and a yellow and red bus'. Find frequency of the letter 'a'

Ex Output:

6