foo.cc: In function 'int main()':
foo.cc:13:18: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::set<int>::size_type' {aka 'long unsigned int'} [-Wformat=]
   13 |         printf("%d\n", s.size());
      |                 ~^     ~~~~~~~~
      |                  |           |
      |                  int         std::set<int>::size_type {aka long unsigned int}
      |                 %ld

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