/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:44:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for( register int i = 0; i < G[ u ].size(); ++i ){
                           ~~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'void check()':
/in/foo.cc:54:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for( register int j = 0; j < G[ i ].size(); ++j ){
                             ~~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'void bfs()':
/in/foo.cc:78:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for( register int i = 0; i < G[ x ].size(); ++i ){
                             ~~^~~~~~~~~~~~~~~