var s: string;
    i, count, max, start, number, maxstart: integer;
    c: char;

begin
 readln(s);
 s:=s+' ';
 count:=1;
 max:=0;
 number:=1;
 c:=s[1];
 for i:=2 to length(s) do
  begin
   if c = s[i] then
    begin
     Inc(count);
    end
   else
    begin
     if count > max then
      begin
       maxstart:=start;
       max:=count;
      end;
     count:=1;
     start:=i;

    end;
   c:=s[i];
  end;
 for i:=maxstart to maxstart + max - 1 do
  write(s[i]);
 readln;
end.