foo.cc: In function 'long int ks(long int, long int)':
foo.cc:20:10: error: 'pow' was not declared in this scope
   return pow(a, n - 1) * a;
          ^~~
foo.cc:20:10: note: suggested alternative: 'putw'
   return pow(a, n - 1) * a;
          ^~~
          putw
foo.cc:23:10: error: 'pow' was not declared in this scope
   return pow(a, n / 2) * pow(a, n / 2);
          ^~~
foo.cc:23:10: note: suggested alternative: 'putw'
   return pow(a, n / 2) * pow(a, n / 2);
          ^~~
          putw

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