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

Ex Input:
Sentence: 'three young children playing with a ball in front of a huge bridge'. Find frequency of the letter 'e'

Ex Output:
5


Ex Input:
Sentence: 'a blue tripocal bird is perched on a wooden fence'. Find frequency of the letter 'd'

Ex Output:
3


Ex Input:
Sentence: 'a beautiful young woman hitting a tennis ball with a racquet'. Find frequency of the letter 'y'

Ex Output:

1