foo.cc: In function 'int main()':
foo.cc:21:22: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |         for(int i=1;i<s.size();i++){
      |                     ~^~~~~~~~~

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