#include <iostream>
#include <stdlib.h>
using namespace std;
int main(){
int *a = NULL;
int n;
int i=0,sum=0,avg=0,count=0,d;
cin >> n;
if(n>10000)
exit(0);
while(n!=-1)
{
i=0;
count=0;
sum=0;
a = new int[n];
d=n;
if(n<2)
exit(0);
while(d--){
cin >> a[i];
if(a[i]>=1000)
exit(0);
sum+=a[i++];
}
if(sum%n==0){
avg = sum/n;
for(i=0;i<n;i++){
d = abs(a[i]-avg);
if(a[i]<avg){
a[i] = a[i]+d;
count+=d;
}
else if(a[i>avg]){
a[i] = a[i]-d;
}
else{
continue;
}
}
cout << count << endl;
}
else
cout << -1 << endl;
cin >> n;
}//EOF
delete [] a;
a = NULL;
}
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