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: 'seagulls sit on the posts of a seaside balcony by a clock tower'. Find frequency of the letter 'g'

Ex Output:
1


Ex Input:
Sentence: 'a canadian airplane on a run way next to a military style aircraft'. Find frequency of the letter 'r'

Ex Output:

5