#include <bits/stdc++.h>

int n, a[20];
double dp[1 << 10][401][2];
bool vis[1 << 10][401];

double * solve(int s, int d) {
    if(vis[s][d + 200])
        return dp[s][d + 200];
    vis[s][d + 200] = true;
    double *cdp = dp[s][d + 200];
    int rest = 0;
    for(int i = 0; i < n; ++i) {
        if(~s & (1 << i))
            continue;
        rest += a[i];
    }
    if(d <= 0 && d + rest <= 0) {
        cdp[0] = 0.0;
        cdp[1] = 0.0;
        return cdp;
    }
    if(d > 0 && d - rest > 0) {
        cdp[0] = 1.0;
        cdp[1] = 1.0;
        return cdp;
    }
    cdp[0] = cdp[1] = -1.0;
    for(int i = 0; i < n; ++i) {
        if(~s & (1 << i))
            continue;
        double x = -1.0, y = -1.0;
        double aq = a[i];
        double u = solve(s ^ (1 << i), d + a[i])[1];
        for(int j = 0; j < n; ++j) {
            if(~s & (1 << j))
                continue;
            double v = solve(s ^ (1 << j), d - a[j])[0];
            double ap = a[j];
            double cy = ((ap - 1.) / ap / aq * u + 1. / ap * v) / (1. - (ap - 1.) / ap * (aq - 1.) / aq);
            double cx = ((aq - 1.) / aq / ap * v + 1. / aq * u) / (1. - (aq - 1.) / aq * (ap - 1.) / ap);
            if(y < 0.0 || cy < y || (fabs(cy - y) < 1e-5 && cx < x)) {
                x = cx;
                y = cy;
            }
        }
        if(cdp[0] < 0.0 || x > cdp[0] || (fabs(x - cdp[0]) < 1e-5 && y > cdp[1])) {
            cdp[0] = x;
            cdp[1] = y;
        }
    }
    return cdp;
}

int main() {
    scanf("%d", &n);
    for(int i = 0; i < n; ++i) {
        scanf("%d", a + i);
    }
    printf("%.12f\n", solve((1 << n) - 1, 0)[0]);
    return 0;
}