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

Ex Input:
Sentence: 'a white bathroom sink sitting next to a toilet'. Find frequency of the letter 'i'

Ex Output:
5


Ex Input:
Sentence: 'a birthday cake with a number one and three candle'. Find frequency of the letter 'w'

Ex Output:
1


Ex Input:
Sentence: 'we are looking at an old photo of a young man'. Find frequency of the letter 'u'

Ex Output:

1