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

Ex Input:
Sentence: 'an commercial airline airplane flies above the clouds'. Find frequency of the letter 'n'

Ex Output:
3


Ex Input:
Sentence: 'a bird outside standing on a table looking up'. Find frequency of the letter 'b'

Ex Output:
2


Ex Input:
Sentence: 'a mother elephant is trunking the baby elephant's smile'. Find frequency of the letter 'i'

Ex Output:

3