Determine the mode of a set of data.
A sequence of lines. Each line will contain a non-negative integer no greater than ~100~ and represents one element of the data, except the last line, which contains the single integer ~-1~ and is not part of the data.
The mode of the set of data. If there is more than one mode, output all modes sorted in ascending order on separate lines.
2 3 4 4 -1