program C;

{$APPTYPE CONSOLE}

uses
  SysUtils;
var
  s, x, f, x1: integer;
begin
  readln (x);
  x1 := x;
  s := 0;
  while (x <> 0) do begin
    s := s + x mod 10;
    x := x div 10;
  end;
  if (odd(s)) then
    if (s * s <> x1) then
      writeln (s * s)
    else
      writeln (-1)
  else
    writeln (x1);
  readln;
  readln;
end.