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

Ex Input:
Sentence: 'older man getting ready to swing his bat at a ball on a stand in front of a group of viewers'. Find frequency of the letter 'n'

Ex Output:
7


Ex Input:
Sentence: 'a woman in yellow dress standing next to a horse'. Find frequency of the letter 'l'

Ex Output:
2


Ex Input:
Sentence: 'an image of tour bus driving down the street'. Find frequency of the letter 'i'

Ex Output:

3