Definition: Evaluate the similarity between them and classify them into classes from 0-5 as follows:
0 : The two sentences are completely dissimilar.
1 : The two sentences are not equivalent, but are on the same topic.
2 : The two sentences are not equivalent, but share some details.
3 : The two sentences are roughly equivalent, but some important information differs/missing.
4 : The two sentences are mostly equivalent, but some unimportant details differ.
5 : The two sentences are completely equivalent, as they mean the same thing.

Positive Example 1 -
Input: Sentence 1: A plane is taking off. Sentence 2: An air plane is taking off.
Output: 5

Positive Example 2 -
Input: Sentence 1: A man is playing a large flute. Sentence 2: A man is playing a flute.
Output: 4

Negative Example 1 -
Input: Sentence 1: A man is playing the cello. Sentence 2: A man seated is playing the cello.
Output: 3

Negative Example 2 -
Input: Sentence 1: The man is playing the piano. Sentence 2: The man is playing the guitar.
Output: 0

Now complete the following example -
Input: Sentence 1: A little boy is playing a keyboard. Sentence 2: A boy is playing key board.
Output: 


Output: 4