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

Ex Input:
Sentence: 'a woman throwing a frisbee on a field'. Find frequency of the letter 's'

Ex Output:
1


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

Ex Output:
4


Ex Input:
Sentence: 'a plate with some food and tongs sitting on it'. Find frequency of the letter 'i'

Ex Output:

4