program p1;
var
  x, c, i, lens : Longint;
  s : String;
  
begin
  c := 10;
  Read(x);
  Str(x, s);
  lens := Length(s);
  for i:=1 to lens do
  begin
    case s[i] of
      '1' : if c > 1 then c := 1;
      '3' : if c > 3 then c := 3;
      '5' : if c > 5 then c := 5;
      '7' : if c > 7 then c := 7;
      '9' : if c > 9 then c := 9;
    end;
  end;
  
  if c < 10 then Writeln(c);

end.