/in/foo.cc: In function 'void dfs2(int)':
/in/foo.cc:76:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < tag[x].size(); i ++)
                    ~~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs3(int)':
/in/foo.cc:100:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < tag[x].size(); i ++)
                    ~~^~~~~~~~~~~~~~~