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

Ex Input:
Sentence: 'a golden haired dog looking out of an open window'. Find frequency of the letter 'd'

Ex Output:
4


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 woman in a black outfit walking up a sidewalk'. Find frequency of the letter 'l'

Ex Output:

3