#include <iostream>
using namespace std;
int main(){
    int N, v[1010];
    cin >> N;
    for(int i = 0; i < N; i++){
        cin >> v[i];
    }
    /*if(N == 2){
        cout << ((double)(v[0] + v[1]) / 2) << endl;
    }
    else{*/
        long long double c[1000100];
        //long long double d[1000100];
        for(int i = 0; i < N - 1; i++){
            for(int j = i + 1; j < N; j++){
                c[i] = (double)(v[i] + v[j]) / 2;
                for(int k = 0; k < N; k++){
                    if(k != i && k != j){
                        c[i] = (double)(c[i] + v[k]) / 2;
                    }
                }
            }
        }
        long long double max = c[0];
        for(int i = 1; i < N; i++){
            if(c[i] > max) max = c[i];
        }
        cout << max << endl;
    //}  
    return 0;
}
