program Rec6;
{ recursive double function example    }
{ exemplo de funcao dobra recursiva }
{ Turbo Pascal 7 source        }
{ Free Pascal Source           }
{ Delphi Source                }
{ Joao Paulo Schwarz Schuler   }
{ http://www.schulers.com/jpss }


function RDobra(X:integer):integer;
begin

if X>=0
   then begin
        if X=0
           then RDobra:=0
           else RDobra:=2+RDobra(X-1);
        end
   else RDobra:=-2+RDobra(X+1);

end;

begin
Writeln(RDobra(-10));    { -20 }
Writeln(RDobra(-1));     { -2  }
Writeln(RDobra(0));      { 0   }
Writeln(RDobra(1));      { 2   }
Writeln(RDobra(10));     { 20  }

end.