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

Ex Input:
Sentence: 'a white and blue plate topped with meat and a salad'. Find frequency of the letter 'u'

Ex Output:
1


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

Ex Output:
3


Ex Input:
Sentence: 'a stop sign at an empty intersection in an industrial factory area'. Find frequency of the letter 't'

Ex Output:

7