/in/foo.cc: In function 'void solve()':
/in/foo.cc:14:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   14 |         for(int i=0;i<s.length();i++){
      |                     ~^~~~~~~~~~~
/in/foo.cc:24:30: warning: array subscript has type 'char' [-Wchar-subscripts]
   24 |                         stac[cnt]=s[i];
      |                              ^~~