text: #include<iostream>
  #include<array>
  #include<set>
  
  int main() {
      std::array<int, 20> arr = {1, 1, 2, 3, 4, 5, 4, 3, 2, 2, 3, 6, 7, 8, 9, 9, 9, 9, 15, 15};
      std::multiset<int> myset(arr.begin(), arr.end());
  
      for (int i = 0; i < 10; i++) {
          myset.insert(i);
      }
  
      for (auto i = myset.begin(); i != myset.end(); i++) {
          std::cout << *i << " ";
      }
      std::cout << "\n";
  }
  