It looks like a match problem......but you can't solve it in this way......

  Actually,I don't really know why my program will work.Could someone who got AC tell me?Prove my algorithm is right or show it is wrong.
  contacts me: yym2008@hotmail.com

  By the way,I found some interesting.If you use "read" and "eof" you will WA on test6,but if you use "readln" or "seekeof" instead,you can pass it......

First draw a graph with two adjacent edges
Then add two edges (say x and y), wherever they are. Now find a path connecting these two edges. Say the path goes across the pairs (A1,A2), (B1,B2), (C1,C2), then you can re-combine the pairs, say (x,A1), (A2,B1), (B2,C1), (C2,y). This is always feasible.
Now, just count the number of edges in each component of the given graph. If one or more numbers is odd, the answer is 0, otherwise it's 1.