/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:17:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0, to; i < v[x].size(); i++) {
                     ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int, int)':
/in/foo.cc:27:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0, to; i < v[x].size(); i++) 
                     ~~^~~~~~~~~~~~~