/in/foo.cc: In function 'void solve()':
/in/foo.cc:52:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i<vec.size(); i++)
               ~^~~~~~~~~~~
/in/foo.cc:53:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0; j<vec.size(); j++)
                ~^~~~~~~~~~~
/in/foo.cc:56:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0; j<vec.size(); j++) {
                ~^~~~~~~~~~~
/in/foo.cc:58:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int k=0; k<vec.size(); k++) {
                 ~^~~~~~~~~~~
/in/foo.cc:61:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int l=0; l<vec.size(); l++) {
                  ~^~~~~~~~~~~