/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:37:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < to[now].size(); i++)
                 ~~^~~~~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:52:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < to[now].size(); i++)
                 ~~^~~~~~~~~~~~~~~~