#include 
#include 
#include 

int main() {
  std::unordered_set planets{
    {"Venus"},
    {"Earth"},
    {"Mars"},
  };

  auto it = planets.find("Earth");
  if (it != planets.end()) {
    std::cout << *it << "\n";
  } else {
    std::cout << "No such planet.\n";
  }

  it = planets.find("PlanetX");
  if (it != planets.end()) {
    std::cout << *it << "\n";
  } else {
    std::cout << "No such planet.\n";
  }
}