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

Ex Input:
Sentence: 'a dog laying on the back of a boat in the water'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'a bunch of cows that are in the field'. Find frequency of the letter 'a'

Ex Output:
3


Ex Input:
Sentence: 'a city street at night filled with lots of traffic'. Find frequency of the letter 't'

Ex Output:

8