I believe, that the problem statment is not very clear regarding the output. It will be nice if you clarify that the output should include all the edges from the input, (and I am not sure if they have to be in the same order).

P.S. sorry that I didn't attach the post to the problem

Edited by author 14.01.2007 21:21

What did you do to get rid of "Wrong Answer on test 20" ?

Edited by author 15.01.2007 01:00

If you get WA20 try to read the problem statement one more time

Be very careful about the output (you may exceed the capacity of a pipe )

 Rostislav

P.S.  it's a nice problem :)