/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:14:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<tre[x].size();i++)
              ~^~~~~~~~~~~~~~
/in/foo.cc:13:6: warning: unused variable 'sum' [-Wunused-variable]
  int sum=tre[x].size();
      ^~~