#include <iostream>
#include <iomanip>

using namespace std;

void input(int*,int);
float sum(int*,int );
bool perfect_number(int n);

int main(){
    int* a,n;
    cout<<"Nhap n: ";
    cin>>n;
    a=new int [n];
    input(a,n);
    cout<<fixed<<setprecision(2)<<sum(a,n);
    return 0;
}

void input(int* a, int n){
    cout<<"Nhap "<<n<<" phan tu: "<<endl;
    for(int i=0;i<n;i++)
        cin>>*(a+i);
}

bool perfect_number(int n){
    int sum=0;
    for(int i=n-1;i>=1;i--)
        if(n%i==0)
            sum+=i;
    if(sum==n)
        return 1;
    else
        return 0;
}

float sum(int* a,int n){
   int sum=0,count=0;
   for(int i=0;i<n;i++)
        if(perfect_number(a[i])){
            sum+=a[i];
            count++;
        }
    return (float)sum/count;
}