/in/foo.cc: In function 'std::__cxx11::string solve(std::__cxx11::string&, std::__cxx11::string&, std::__cxx11::string&)':
/in/foo.cc:10:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     while (i < s.size())
            ~~^~~~~~~~~~
/in/foo.cc:23:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         if (j == t.size()) res += u, j = 0;
             ~~^~~~~~~~~~~