CANDY.cpp

#include <iostream>
using namespace std;

int main()
{
	//freopen("input.txt","r",stdin);
	int n = 0;
	while(true)
	{
		cin >> n;
		if(n == -1) break;

		int sum = 0;
		int *a = new int[n];
		for(int i = 0; i < n; i++)
		{
			cin >> a[i];
			sum += a[i];
		}

		int moves = 0;
		if(sum % n != 0) moves = -1;
		else 
		{
			int average = sum / n;
			for(int i = 0; i < n; i++)
				if(a[i] < average) moves += average - a[i];
		}

		cout << moves << endl;
		delete[] a;
	}
	return 0;
}