foo.cc: In function 'int main()':
foo.cc:29:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  int l, r; scanf("%d%d", &l, &r);
            ~~~~~^~~~~~~~~~~~~~~~
foo.cc: In function 'bool is_super_prime(int)':
foo.cc:26:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

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