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

Ex Input:
Sentence: 'a group of tennis players on a tennis court'. Find frequency of the letter 'o'

Ex Output:
4


Ex Input:
Sentence: 'a small white dog looking out a car window'. Find frequency of the letter 'l'

Ex Output:
3


Ex Input:
Sentence: 'three giraffes are leaning over a fence to eat the tree leaves'. Find frequency of the letter 'i'

Ex Output:

2