/in/foo.cc: In function 'int main()':
/in/foo.cc:40:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int i=0;i<G[u].size();i++)
                ~^~~~~~~~~~~~
/in/foo.cc:46:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int j=0;j<G[v].size();j++)
                 ~^~~~~~~~~~~~