foo.cc: In function 'int main()':
foo.cc:28:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   28 | for (int i = 0; i < G[u].size(); i++) {
      |                 ~~^~~~~~~~~~~~~
foo.cc:14:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   14 | scanf("%d%d",&u,&v);
      | ~~~~~^~~~~~~~~~~~~~

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