#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
using namespace std;
#define maxn 1010
struct my{
	long num,time;
}a[maxn];
bool cmp(my a,my b){
	return a.time<b.time;
}
int main()
{
	long n,num=0;
	cin>>n;
    for(int i=1;i<=n;i++){ 
     cin>>a[i].time;
     a[i].num=i; 
	 }
	 
    sort(a+1,a+n+1,cmp);
    long cnt=n-1,sum=0;
    for(int i=1;i<=n;i++,cnt--)
      sum+=cnt*a[i].time;
    
	printf("%.2lf",(double)sum/(double)n);
}