#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N, v;
    cin >> N;
    auto F = [&](int n){
       double num = 0, div = 0, d = 1, d2 = 1;
        for(int i = 0; i < n; i++){
            d *= 0.81;
            d2 *= 0.9;
            num += d;
            div += d2;
        }
        return sqrt(num) / div;
    };
    auto f = [&](int n){
        double a = F(n), b = F(1 << 10);
        return (a - b) / (1 - b) * 1200;
    };
    auto g = [&](int X){
        return pow(2.0, X / 800.0);
    };
    auto inv_g = [&](double X){
        return log2(X) * 800;
    };
    double num = 0, div = 0, d = 1;
    for(int i = 0; i < N; i++){
        cin >> v;
        d *= 0.9;
        num += g(v) * d;
        div += d;
    }
    cout << fixed << setprecision(15) << inv_g(num / div) - f(N) << '\n';
}