/*The input file consists of several blocks of data. Each block starts with the number of candy packets N(1<= N <=10000)
followed by N integers (each less than 1000)in separate lines,
giving the number of candies in each packet. After the last block of data there is the number -1. */
#include<iostream>
#include <cstdlib>
#include<string.h>
using namespace std;
int main()
{
  long long count=0,j,i,sum=0,l,temp,t;
 double k;
    cin>>k;
    while(k!=-1&&k<=10000)
    {
        int n=(int)k;
         int a[1005];
         for(i=0;i<n;i++)
         {
                         cin>>a[i];
                         sum+=a[i];
                         }
                         temp=sum/n;
                         t=n*temp;
                      // int temp1=(int)temp;
                      // l=sum%n;
                         if(t==sum)
                         {
                         for(j=0;j<n;j++)
                         {
                                         if(a[j]>temp)
                                         count+=a[j]-temp;
                                         }
                                         cout<<count<<endl;
                                         }
                                         else
                                         cout<<-1;
                                         count=0;
                                         sum=0;
                                         cin>>k;
                                         }

cin.clear();
cin.ignore(255,'\n');
cin.get();

return 0;
}