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

typedef long long   signed int LL;
typedef long long unsigned int LU;

#define incID(i, l, r) for(int i = (l)    ; i <  (r); i++)
#define incII(i, l, r) for(int i = (l)    ; i <= (r); i++)
#define decID(i, l, r) for(int i = (r) - 1; i >= (l); i--)
#define decII(i, l, r) for(int i = (r)    ; i >= (l); i--)
#define  inc(i, n) incID(i, 0, n)
#define inc1(i, n) incII(i, 1, n)
#define  dec(i, n) decID(i, 0, n)
#define dec1(i, n) decII(i, 1, n)

#define inII(v, l, r) ((l) <= (v) && (v) <= (r))
#define inID(v, l, r) ((l) <= (v) && (v) <  (r))

#define PB push_back
#define EB emplace_back
#define MP make_pair
#define FI first
#define SE second
#define UB upper_bound
#define LB lower_bound
#define PQ priority_queue

#define  ALL(v)  v.begin(),  v.end()
#define RALL(v) v.rbegin(), v.rend()
#define  FOR(it, v) for(auto it =  v.begin(); it !=  v.end(); ++it)
#define RFOR(it, v) for(auto it = v.rbegin(); it != v.rend(); ++it)

template<typename T> bool   setmin(T & a, T b) { if(b <  a) { a = b; return true; } else { return false; } }
template<typename T> bool   setmax(T & a, T b) { if(b >  a) { a = b; return true; } else { return false; } }
template<typename T> bool setmineq(T & a, T b) { if(b <= a) { a = b; return true; } else { return false; } }
template<typename T> bool setmaxeq(T & a, T b) { if(b >= a) { a = b; return true; } else { return false; } }
template<typename T> T gcd(T a, T b) { return (b == 0 ? a : gcd(b, a % b)); }
template<typename T> T lcm(T a, T b) { return a / gcd(a, b) * b; }

// ---- ----

int n;
double a[100], FF = 0.229438124492144902470153351;

double F(int x) {
	double v1 = 0.0;
	double v2 = 0.0;
	inc1(i, x) {
		v1 += pow(0.81, i);
		v2 += pow(0.90, i);
	}
	return sqrt(v1) / v2;
}

double f(int x) {
	return 1200 * (F(x) - FF) / (F(1) - FF);
}

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

double gi(double y) {
	return 800.0 * (log(y) / log(2.0));
}

int main() {
	cin >> n;
	inc(i, n) { cin >> a[i]; }
	
	// (745.4/1200)
	// (sqrt(0.81 + 0.81^2)/(0.9 + 0.81))
	// 0.229438124492144902470153351078389912779905395445868470863
	
	double v1 = 0.0;
	double v2 = 0.0;
	inc1(i, n) {
		v1 += pow(0.9, i) * g(a[i - 1]);
		v2 += pow(0.9, i);
	}
	
	// cout << "f(2) = " << f(2) << endl;
	
	LL ans = gi(v1 / v2) - f(n);
	cout << ans << endl;
	
	return 0;
}