#include <iostream>
#include <omp.h>

using namespace std;

void Greeting();

int main() {

     omp_set_max_active_levels(2);

     #pragma omp parallel num_threads(4) 
     {
         int id{omp_get_thread_num()};
         #pragma omp critical
         {
             cout << "Hello world from " << id <<   endl;
         }

         #pragma omp parallel  num_threads(4) if (id % 2 )
         {
            int newid{omp_get_thread_num()};
            #pragma omp critical
            {
                 cout << "More deeply parallel " << id << " and "
                      << newid << endl;
            }
         }

         #pragma omp barrier
         cout << endl << endl;

         #pragma omp for 
         for(int i = 0; i < 20; ++i) {
             #pragma omp critical 
             {
                cout << id << " i = " <<  i << endl;
             }
         }
     }

     return 0;
}