#include <iostream>

class ForwardDeclClass1;


namespace a {
   
   class ForwardDeclClass2;
   
   
   class RegularClass1 {
      
   };
   
   
   namespace b {
      
      class ForwardDeclClass3;
      
      
      class RegularClass2 {
         
      };
      
      
      namespace c {
         
         class ForwardDeclClass4;
         
         
         class RegularClass3 {
            
         };
      
      }
   
   }

}

int main(int argc, char *argv[]) {
   std::cout << "Hello World!" << std::endl;
   
   return 0;
}
