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

Ex Input:
Sentence: 'a downhill skier with snow plumes behind them'. Find frequency of the letter 'i'

Ex Output:
4


Ex Input:
Sentence: 'a black horse with a white dot on its forehead'. Find frequency of the letter 't'

Ex Output:
4


Ex Input:
Sentence: 'a large group of people in winter clothing gathered outside a building'. Find frequency of the letter 'g'

Ex Output:

5