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

Ex Input:
Sentence: 'a tennis player that is running to get the tennis ball'. Find frequency of the letter 't'

Ex Output:
7


Ex Input:
Sentence: 'a person is riding in a cart pulled by a horse'. Find frequency of the letter 'a'

Ex Output:
4


Ex Input:
Sentence: 'several people standing outside of a red train'. Find frequency of the letter 'e'

Ex Output:

6