#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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5
1
1
1
1
6
2
3
4
2
8
4
5
1
1
1
1
6
5
4
2
2
1
1
3
4
3
5
5
34
31
44
89
62
5
345
313
445
894
622
-1