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

Ex Input:
Sentence: 'two little girls playing with a bat and a tennis ball'. Find frequency of the letter 'w'

Ex Output:
2

Ex Input:
Sentence: 'a dog on a couch near many pillows'. Find frequency of the letter 'p'

Ex Output:
1

Ex Input:
Sentence: 'a man spins a frisbee on his finger'. Find frequency of the letter 'i'

Ex Output:
4