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

Ex Input:
Sentence: 'a crowd of people skiing and enjoying the snow'. Find frequency of the letter 'o'

Ex Output:
5


Ex Input:
Sentence: 'a gray colored pigeon that is perched on a railing outside of a building, with other buildings in the background'. Find frequency of the letter 'e'

Ex Output:
7


Ex Input:
Sentence: 'a lady carrying a birthday cake and two other ladies'. Find frequency of the letter 'i'

Ex Output:

3