#include<iostream>
#using namespace std;

double calculateGPA(int n) {
    double sum = 0;
    for(int i=0; i< n; i++) {
        double grade;
        cin >> grade;
        if (grade < 0) {
            throw "Invalid input";
        }
        sum += grade;
    }
    return sum/n;
]

int main() {
    int n;
    cin >> n;
    
    try {
        double gpa = calculateGPA(n);
        cout << gpa << endl;
    }
    catch (const char* msg) {
        cout << msg << endl;
    }
    return 0;
}