#include <iostream>
#include <iomanip>

using namespace std;

int main()
{
	int tab[100];
	int x = 0, n = 0, sum = 0;

	cin >> x;
	while(x >= 0)
	{
		tab[n] = x;
		n++;
		cin >> x;
	}
	int length = n;

	for(int i = 0; i < length; i++)
	{
		sum += tab[i];
	}

	float moy = (float)sum / length;
	cout << setiosflags(ios::fixed | ios::showpoint) 
	     << setprecision(2)
	     << moy << '\n';

	return 0;
} // main()