{ здесь is_palindrom из FAQ-а }

type
  PT = ^T;
  T = array[1 .. 1] of longint;
var
  arr: PT;
  n, count, i: integer;
  X: longint;
begin
  write('n = '); readln(n);
  getmem(arr, n * sizeof(longint));
  count := 0;
  while not eoln do begin
    read(X);
    if is_palindrom(X) then begin
      inc(count); arr^[count] := X;
    end;
  end;

  for i := 1 to count do
    writeln(arr^[i]);
  freemem(arr, n * sizeof(longint))
end.

function space(s: string): boolean;
begin
  space := (s[1] = ' ') and (s[length(s)] = ' ');
end;
function trim(s: string): string;
begin
  while (s <> '') and (pos(' ', s) > 0) do
    delete(s, pos(' ', s), 1);

  trim := s;
end;
function revert(s: string): string;
var
  rev: string;
  i: integer;
begin
  rev := '';
  for i := 1 to length(s) do rev := s[i] + rev;
  revert := rev;
end;

var
  i, j: integer;
  s, st, max_s: string;

begin
  {
    s := '1 2 2 1 0 7';
    s := '1 2 2 1 33 21 12 33 1 5';
    s := '1 2 2 1 33 21 12 373 1 5';
  }
  readln(s);

  s := ' ' + s + ' ';

  max_s := '';
  for i := 1 to length(s) - 1 do begin
    for j := 1 to length(s) - i do begin
      st := copy(s, i, j);
      if space(st) and (trim(st) = revert(trim(st))) then begin
        if length(max_s) < length(st) then max_s := st;
      end;
    end;
  end;
  writeln(max_s);
end.