foo.cc: In function 'void mul(int)':
foo.cc:13:14: error: 'sqrt' was not declared in this scope
  for (i=2;i<=sqrt(q)+1;i++)
              ^~~~
foo.cc:13:14: note: suggested alternative: 'qsort'
  for (i=2;i<=sqrt(q)+1;i++)
              ^~~~
              qsort
foo.cc: In function 'void d(int)':
foo.cc:27:19: error: 'sqrt' was not declared in this scope
  for (i = 2; i <= sqrt(q) + 1; i++)
                   ^~~~
foo.cc:27:19: note: suggested alternative: 'qsort'
  for (i = 2; i <= sqrt(q) + 1; i++)
                   ^~~~
                   qsort

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