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

Ex Input:
Sentence: 'young girl playing with refrigerator magnet while kneeling on floor'. Find frequency of the letter 'n'

Ex Output:
6


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

Ex Output:
3


Ex Input:
Sentence: 'an airliner is preparing to take off at the tarmac'. Find frequency of the letter 'n'

Ex Output:

3