>>19
#include <iostream>
#include <iomanip>
int main(void)
{
int i, n, sum;
n = sum = 0;
while(1)
{
std::cin >> i;
if (i == 0)
break;
sum += i;
n++;
}
std::cout << std::fixed << std::setprecision(2) <<
(double)sum / n << std::endl;
return 0;
}