/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:8:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<road[x].size();++i)
              ~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'void chu(int, int)':
/in/foo.cc:20:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<road[x].size();++i)
              ~^~~~~~~~~~~~~~~