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

Ex Input:
Sentence: 'a man in a sweatshirt is taking his own picture'. Find frequency of the letter 'u'

Ex Output:
1


Ex Input:
Sentence: 'a group of cars and house on truck passing in a street'. Find frequency of the letter 'i'

Ex Output:
2


Ex Input:
Sentence: 'a man holding a tennis racquet on top of a tennis court'. Find frequency of the letter 't'

Ex Output:

5