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

Ex Input:
Sentence: 'a stop sign near a rail road crossing sign'. Find frequency of the letter 'g'

Ex Output:
3


Ex Input:
Sentence: 'a log in the water with three birds perched on it'. Find frequency of the letter 'r'

Ex Output:
4


Ex Input:
Sentence: 'a long blue articulated bus waits in traffic in this european city'. Find frequency of the letter 't'

Ex Output:

6