#include <iostream>
#include <vector>
#include <cmath>
using namespace std;
vector<int> RP;
double g(double X){
	return pow(2.0,X/800);
}
double ga(double X){
	return 800*(log2(X));
}
double F(int n){
	double P = 0;
	double C = 0;
	for(int i = 1; n >= i; i++){
		P+=pow(0.81,i);
		C+=pow(0.9,i);
	}
	return sqrt(P)/C;
}
double f(int n){
	return 1200*((F(n)-0.229417)/(F(1)-0.229417));
}
double Rating(int n){
	double R = 0;
	double P = 0;
	double C = 0;
	for(int i = 1; n >= i; i++){
		P+=g(RP[i-1])*pow(0.9,i);
		C+=pow(0.9,i);
	}
	R+=ga(P/C);
	R-=f(n);
	return R;
}

int main(){
	// for(int i = 1; 10 > i; i++){
	// 	cout << f(i) << endl;
	// }
	int n;cin>>n;
	int r;
	for(int i = 0; n > i; i++){
		int t;cin>>t;RP.push_back(t);
		r=Rating(i+1);
	}
	cout << r << endl;
}