#include <iostream>
#include <iomanip>
#include <vector>
using namespace std;

typedef unsigned long long ullong;

int main()
{
	int x = 0, n = 0, length = 0;
	ullong somme = 0;

	cin >> x;
	somme += x;
	while(x >= 0)
	{
		somme += x;
		n++;
		cin >> x;
	}
	length = n;
	float moy = (float)somme / length;
	cout << setiosflags(ios::fixed | ios::showpoint) 
	     << setprecision(2)
	     << moy << endl;

	return 0;
} // main()