/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:18:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0; i < G2[s].size(); i++) {
                  ~~^~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:60:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < Vex.size(); i++) {
                   ~~^~~~~~~~~~~~