Bugs fixed in the checker program.

1. The total length of dangerous segments was not always correctly verified against the canonical answer. Most prominently, the following output was previously accepted for the sample input (test 1), which has the total dangerous length 1.0 with the optimal one being 0.8:

2
1.0 1.5
0.0 1.5

2. Precision issues were fixed that were causing solutions with certain output rounding strategies being rejected (most commonly, WA8).

The limitation on the number of pieces of furniture N was updated in the problem statements from N >= 0 to N >= 1 to reflect the actual test data.

Additionally, the time limit was reduced from 2.0 sec to 1.0 sec.

All solutions have been rejudged. 21 authors lost, and 2 other authors gained the Solved status for the problem.