void dg(int k){
if(k==4){
cout<<"4,5-->9,10"<<endl;
cout<<"8,9-->4,5"<<endl;
cout<<"2,3-->8,9"<<endl;
cout<<"7,8-->2,3"<<endl;
cout<<"1,2-->7,8"<<endl;
}
else{
cout<<k<<","<<k+1<<"-->"<<2*k+1<<","<<2*(k+1)<<endl;
cout<<2*k-1<<","<<2*k<<"-->"<<k<<","<<k+1<<endl;
dg(k-1);
}
}