begin
   int xx, y;
   read x;
   read y;
   if 0=x*x+y*y then write 0-1
   else begin
      int x, y;
      if x<0 then x:=0-x; else;
      if y>=0 then else y:=0-y;
      while x*y\=0 do if x>y then x:=x--y else y:=y-x
      write x+y;
   end
end