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

Ex Input:
Sentence: 'a construction sign is displayed on a street'. Find frequency of the letter 'i'

Ex Output:
4


Ex Input:
Sentence: 'an elephant with broken tusks stands in front of a hill and boulders'. Find frequency of the letter 'n'

Ex Output:
7


Ex Input:
Sentence: 'the small girl focuses on the goal before kicking the ball'. Find frequency of the letter 'u'

Ex Output:

1