#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>

using namespace std;
 
double mean(const vector<int>& numbers) {
    if (numbers.empty())
        return 0;
    return accumulate(numbers.begin(), numbers.end(), 0.0) / numbers.size();
}

int main() {

    int input;
    vector<int> v;
    while(cin >> input){
        v.push_back(input);
    }

    cout << mean(v);

	return 0;

}