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

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: 'a street scene looking at the back of the stop sign'. Find frequency of the letter 't'

Ex Output:
6


Ex Input:
Sentence: 'a man riding a skateboard outside of a building'. Find frequency of the letter 'u'

Ex Output:

2