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

Input: Consider Input: Sentence: 'a snow filled mountain with a guy with ski's'. Find frequency of the letter 'f'

Output: 1

Input: Consider Input: Sentence: 'a tennis player after hitting a shot back to the other side of the court'. Find frequency of the letter 'n'

Output: 3

Input: Consider Input: Sentence: 'a man setting up a large inflatable balloon outside'. Find frequency of the letter 'm'
Output: 1