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.

Example Input: Sentence 1: A mostly black train on a track. Sentence 2: A car parked in front of train tracks.
Example Output: 1

Example Input: Sentence 1: Prince is replacing Sanford "Sandy" Weill, who will remain Citigroup's chairman. Sentence 2: Prince, who heads Citigroup's global corporate and investment bank, is replacing Sanford Weill as CEO.
Example Output: 3

Example Input: Sentence 1: The American Stock Exchange biotech index .BTK surged 5 percent. Sentence 2: The Philadelphia Stock Exchange's semiconductor index .SOXX jumped 6.10 percent.
Example Output:
1