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 river with a long dragon boat in it and rowers on the boat in sets of two, along with two other people'. Find frequency of the letter 'h'

Ex Output:
4


Ex Input:
Sentence: 'a herd of giraffes in tall african grass'. Find frequency of the letter 'a'

Ex Output:

6