#include <bits/stdc++.h>
using namespace std;
int main()
{
	int n;
	cin >> n;
	int temp;
	double sum = 0;
	for (int i = 1; i <= n; i++)
	{
		cin >> temp;
		sum += temp;
	}
	printf("%.2lf",sum / 2);
	return 0;
}