#11 出错 求调

#include<stdio.h>
int a[105],n,divide;
bool is[105],bridge[105];
int work(int l,int r){
	int mid=l+1;
	while(l>0&&r<=n){
		if(a[l]<divide) return l;
		if(a[r]<divide) return r;
		l--,r++;
	}
	while(l>0){
		if(a[l]<divide) return l;
		l--;
	}
	while(r<=n){
		if(a[r]<divide) return r;
		r++;
	}
	return mid;
}
bool shift(){
	for(int i=1;i<=n;i++) if(a[i]!=divide) return 0;
	return 1;
}
int main(){
	int sum=0,ans=0;
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d",&a[i]);
		sum+=a[i];
	}
	if((sum/n)*n!=sum){
		puts("-1");
		return 0;
	}
	divide=sum/n;
	for(int i=1;i<=n;i++) if(a[i]!=divide) is[i]=1;
	while(!shift()){
		for(int i=1;i<=n;i++){
			if(!is[i]||a[i]<divide) continue;
			int q=work(i-1,i+1);
			for(int j=i-1;j>=q;j--){
				if(bridge[j]) continue;
				bridge[j]=1,ans++;
			}
			for(int j=i+1;j<=q;j++){
				if(bridge[j]) continue;
				bridge[j]=1,ans++;
			}
			if(q==i) break;
			if(a[i]-divide>divide-a[q]) a[i]-=divide-a[q],a[q]=divide,is[q]=0;
			else a[q]+=a[i]-divide,a[i]=divide,is[i]=0;
			break;
		}
	}
	printf("%d\n",ans);
	return 0;
}