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

Ex Input:
Sentence: 'a man in a black wet suit rides an orange surfboard on the water'. Find frequency of the letter 'o'

Ex Output:
3


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: 'motorcycle parked at a rest stop overlooking a settled valley'. Find frequency of the letter 't'

Ex Output:

6