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

double F(int n) {
    double nu=sqrt(0.81*(1-pow(0.81,n))/0.19);
    double de=0.9*(1-pow(0.9,n))/0.1;
    return nu/de;
}

double f(int n) {
    double Finf=sqrt(0.81/0.19)/9;
    return (F(n)-Finf)/(F(1)-Finf)*1200;
}

double g(int x) {
    return pow(2.0,x/800.0);
}

double rg(double x) {
    return 800*log2(x);
}

int main() {
    int n;
    cin>>n;
    int rp[n];
    for (int i=0;i<n;i++)
        cin>>rp[i];
    double nu=0;
    for (int i=0;i<n;i++)
        nu+=g(rp[i])*pow(0.9,i+1);
    double de=0.9*(1-pow(0.9,n))/0.1;
    cout<<rg(nu/de)-f(n)<<endl;
    return 0;
}