I've used the algorithm for bipartite graph to this
problem,and it got WA.So i refer to some graph theory
book,it says that we must handle blossoms,but it did not
say why this!From my test data the bipartite graph
algorithm works fine!Can anybody explain this to me?Or give
out some counter examples that the bipartite graph
algorithm fails...

I asked about this problem. There are some "flowers" things
that make the bipartite algorithm to fail. IT's based on
a true theorem, but the DFS fails. However, I do the
following thing - DFS, but observse the edges in random
way, not for(i=1;i<=n;i++) and things like that but a
permutation.
Damn, i think my English is not good :)))

I have generated case(not randomly) where your solution
fails. But it is not uploaded, expect rejudge.