var n,a,b,aux:longint;
procedure citire;
          begin
               assign(input,'nunta.in');
               reset(input);
               read(input,n);
               close(input)
          end;
procedure gasire;
          var i:longint;
          begin
                assign(output,'nunta.out');
                rewrite(output);
                if n=1 then write(output,1)
                else if n=2 then write(output,2)
                else if n=3 then write(output,3)
                else begin
                a:=2;
                b:=3;
                for i:=3 to n do begin
                    aux:=a+b;
                    a:=b;
                    b:=aux
                    end;
                    write(output,b)
                    end;
                close(output)
          end;
begin
     citire;
     gasire
end.