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. \InputFile The first line contains the number of nails $n~(2 \le n \le 100)$. The next line contains $n$ numbers --- the coordinates of all the nails (non-negative integers not exceeding $10000$). \OutputFile Print the minimum total length of all threads.