Some nails are hammered on a straight plank. Any two nails can be joined by a thread. Connect some pairs of nails with a thread, so that to each nail will be tied with at least one thread, and the total length of all threads will be minimal.
The first line contains the number of nails . The next line contains numbers — the coordinates of all the nails (non-negative integers not exceeding ).
Print the minimum total length of all threads.