#include <bits/stdc++.h>
using namespace std;
int n , m , k , a[300001];
long long cnt;
double ans;

int main()
{
	cin>>n;
	for(int i = 0 ; i < n ; i++)
	{
		cin>>a[i];
		cnt += a[i];
	}
	ans = pow(cnt,2) / n;
	cout<<fixed<<setprecision(8)<<ans;
	
	return 0;
}

q1:为啥0pts

q2:cnt*cnt和pow(cnt,2)有啥区别