## IPSC 2002

## Problem S – Candy

Jennifer is a teacher in the first year of a primary school.
She has gone for a trip with her class today. She has taken a packet
of candies for each child. Unfortunately, the sizes of the packets are not
the same.

Jennifer is afraid that each child will want to have the
biggest packet of candies and this will lead to quarrels or even
fights among children. She wants to avoid this. Therefore, she
has decided to open all the packets, count the candies in each
packet and move some candies from bigger packets to smaller ones
so that each packet will contain the same number of candies. The
question is how many candies she has to move.

### Input file specification

The input file consists of
several blocks of data. Each block starts with the number of candy
packets **N** followed by **N** integers giving the number
of candies in each packet. After the last block of data there is
the number -1.

### Output file specification

The output file should
contain one line with the smallest number of moves for each block of data.
One move consists of taking one candy from a packet and putting it into
another one. If it is not possible to have the same number of candies in
each packet, output the number -1.

### Example

**Input file:**
5
1 1 1 1 6
2
3 4
-1

**Output file:**
4
-1