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

Ex Input:
Sentence: 'an elephant with broken tusks stands in front of a hill and boulders'. Find frequency of the letter 'n'

Ex Output:
7


Ex Input:
Sentence: 'a little boy that has a toothbrush in his mouth'. Find frequency of the letter 'r'

Ex Output:
1


Ex Input:
Sentence: 'a french dip is shown with cilantro and onions'. Find frequency of the letter 'a'

Ex Output:

3