#pragma region include
#include <iostream>
#include <iomanip>
#include <stdio.h>

#include <sstream>
#include <algorithm>
#include <cmath>
#include <complex>

#include <string>
#include <cstring>
#include <vector>
#include <tuple>
#include <bitset>

#include <queue>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <list>

#include <fstream>
#include <random>
//#include <time.h>
#include <ctime>
#pragma endregion //#include
/////////
#define REP(i, x, n) for(int i = x; i < n; ++i)
#define rep(i,n) REP(i,0,n)
#define ALL(X) X.begin(), X.end()
/////////
#pragma region typedef
typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
typedef std::pair<LL,LL> PLL;//
typedef std::pair<int,int> PII;//
#pragma endregion //typedef
////定数
const int INF = (int)1e9;
const LL MOD = (LL)1e9+7;
const LL LINF = (LL)1e18+20;
const double PI = acos(-1.0);
const double EPS = 1e-9;
/////////
using namespace::std;

const double F_inf = 0.22943812449214490247015335107611;
double F(int N){
	double res = 0;
	for(int i=1;i<=N;++i){
		res += pow(0.81,i);
	}
	double ans = 0;
	ans = sqrt( res );

	res = 0;
	for(int i=1;i<=N;++i){
		res += pow(0.9, i);
	}
	ans /= res;
	
	return ans;
}

double f(int N){
	//double res1 = F(N)/F(1) * 1200;
	double res1 = (F(N)-F_inf)/(F(1)-F_inf) * 1200;
	return res1;
}
double g(double X){
	return pow(2.0, X/800);
}
double g_inv(double Y){
	double res = log(Y)/log(2.0) * 800;
	return res;
}

void solve(){
	int N;
	cin >> N;
	vector<double> RPerf(N+1);
	for(int i=1;i<=N;++i){
		cin >> RPerf[i];
	}
	double Y = 0;
	double res = 0;
	for(int i=1;i<=N;++i){
		res += g(RPerf[i]) * pow(0.9,i);
	}
	double res2 = 0;
	for(int i=1;i<=N;++i){
		res2 += pow(0.9, i);
	}
	Y = res/res2;
	
	double ans;
	ans = g_inv(Y) - f(N);
	cout << ans << endl;
	//cerr << f(2) << endl;
}

#pragma region main
signed main(void){
	std::cin.tie(0);
	std::ios::sync_with_stdio(false);
	std::cout << std::fixed;//小数を10進数表示
	cout << setprecision(16);//小数点以下の桁数を指定//coutとcerrで別	

	solve();
}
#pragma endregion //main()