SPOJ Problem 2123:Candy I

#include<cstdio>
#include<cstring>
int n,i,j,p,s;
int a[10001];
int abs(int p){return p>0?p:-p;}
int main(){
    while(scanf("%d",&n)&&n!=-1){
        p=0;
        for (i=1;i<=n;i++){
            scanf("%d",&a[i]);
            p+=a[i];
        }
        if (p%n)printf("-1\n");else{
            s=0;
            p/=n;
            for(i=1;i<=n;i++)
                s+=abs(a[i]-p);
            s/=2;
            printf("%d\n",s);
        }
    }
}