#include<iostream>
using namespace std;
class statistics{
    private:
    double mean;
    public:
    statistics(int arr[], int n){
        if (n <=0){
            mean =-1;
            return;
        }
    }
    int sum = 0;
    for(int i = 0; i<n ; i++){
        sum += arr[i];
    }
    mean = (double)sum/n;
}
statistics(const statistics &obj)
{
    mean = obj.mean;
}
void display(){
    if(mean ==-1)
    cout<<"invalid input";
    else
    cout<<mean;
}
};
int main(){
    int n;
    cin >> n;
    if (n<0){
        cout<<"invalid input";
        return 0;
    }
    int arr[n];
    for(int i=0; i<n;i++){
        cin>>arr[i];
    }
    statistics obj1(arr,n);
    statistics obj2=obj1;
    
    obj2.display();
    return 0 ;
}