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

Ex Input:
Sentence: 'a gray elephant is in a grassy field'. Find frequency of the letter 'e'

Ex Output:
3


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: 'passengers stand at the back of a bus loaded with luggage'. Find frequency of the letter 'a'

Ex Output:

7