/in/foo.cc: In function 'void tarjan(int)':
/in/foo.cc:20:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < cows[id].way.size(); i++)
                     ~~^~~~~~~~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:61:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int j = 0; j < cows[a].way.size(); j++)
                         ~~^~~~~~~~~~~~~~~~~~~~
/in/foo.cc:84:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int j = 0; j < cows[i].way.size(); j++)
                         ~~^~~~~~~~~~~~~~~~~~~~