#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

#define REP(i,n) for(int i=0;i<n;++i)
#define SORT(name) sort(name.begin(), name.end())
#define ZERO(p) memset(p, 0, sizeof(p))
#define MINUS(p) memset(p, -1, sizeof(p))

#define MOD 1000000007
#define INF 1000000000

double F(int n) {
    double child = 0;
    double par = 0;
    for(int i = 1; i <= n; ++i) {
        child += pow(0.81, (double)i);
        par += pow(0.9, (double)i);
    }
    child = sqrt(child);
    return child / par;
}
double f(int n) {
    double child = F(n);
    double par = F(1);
    return child * 1200 / par;
}
double inv_g(double x) {
    return 800 * log2(x);
}
double g(double x) {
    return pow(2.0, x / 800);
}

int N;
double rperf[200];
int main()
{
    cin >> N;
    for(int i = 1; i <= N; ++i) {
        cin >> rperf[i];
    }
    double x;
    double child = 0;
    double par = 0;
    for(int i=1; i <= N; ++i) {
        child += g(rperf[i]) * pow(0.9, (double)i);
        par += pow(0.9, (double)i);
    }
    x = child / par;
    printf("%f\n", inv_g(x) - f(N));


    return 0;
}