/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:16:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<to[v].size();i++){
              ~^~~~~~~~~~~~~
/in/foo.cc: In function 'void work()':
/in/foo.cc:31:6: warning: unused variable 'tt' [-Wunused-variable]
  int tt=-1;
      ^~