#include<bits/stdc++.h>
#define MAX 5001
#define INF 18000001
using namespace std;
double arr[MAX];
double dp[MAX];

double min(double a , double b)
{
	if(a < b)
		return a;
	return b;
}

int main()
{
	ios::sync_with_stdio(0);
	int n;
	cin >> n;
	if(n % 2 == 0)
		cout << 1/0;
	for(int i = 0;i < n;i++)
	{
		cin >> arr[i];
	}

	if(n == 1)
	{
		cout << arr[0];
		return 0;
	}
	sort(arr , arr+n);
	dp[0] = arr[0];
	dp[1] = arr[0] / 2 + arr[1];
	dp[2] = min(dp[1] + arr[2] , arr[1] + arr[2]);
	for(int i = 3;i < n;i++)
	{
		dp[i] = min((dp[i-2] + arr[i-1] /2+arr[i]) , min((dp[i-3] + arr[i-1]+arr[i]) , (dp[i-1] + arr[i])));

	}
	cout.precision(2);
	cout<<fixed << dp[n - 1];
}