foo.cc: In function 'void spfa(int)':
foo.cc:58:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   58 | for( i = 0 ; i < linker[ now ].size() ; i++ )
      |              ~~^~~~~~~~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:80:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   80 | scanf( "%d %d" , &n , &m );
      | ~~~~~^~~~~~~~~~~~~~~~~~~~~
foo.cc:83:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   83 | scanf( "%d %d %d %d" , &e[i].x , &e[i].y , &e[i].a , &e[i].b );
      | ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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