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: 'a yellow and green train on a train track in a wooded area'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'a bowl of oranges sitting on a wooden cutting board'. Find frequency of the letter 'g'

Ex Output:

3