var
  x, min, max, digit: integer;

begin
  readln(x);
  max := -1;
  min := 10;
  while (x > 0) do
  begin
    digit := x mod 10;
    if (digit mod 2 = 0) and (digit > max) then
      max := digit;
    if (digit mod 2 <> 0) and (digit < min) then
      min := digit;
    x := x div 10;
  end;
  if (max <> -1) then
    writeln(max);
  if (min <> 10) then
    writeln(min);
end.