foo.cc: In function 'void selve(int)':
foo.cc:13:31: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   13 |         if(s1.size()+s2.size()==n)a[++t]=r1;
      |            ~~~~~~~~~~~~~~~~~~~^~~
foo.cc:16:31: warning: comparison of integer expressions of different signedness: 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   16 |         if(s1.size()+s2.size()==n)a[++t]=r2;
      |            ~~~~~~~~~~~~~~~~~~~^~~

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