#include <bits/stdc++.h>

int n;
int w[22];
double f[1 << 22];

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) scanf("%d", &w[i]);
    for (int mask = 0; mask < 1 << n; mask++) {
        const int t = __builtin_popcount(mask);
        if (t <= 1) continue;
        std::vector<double> a, b;
        for (int i = 0; i < n; i++)
            if (mask >> i & 1) {
                a.push_back(w[i]);
                b.push_back(f[mask ^ (1 << i)]);
            }
        double max = 0;
        double sum1 = 0, sum0 = -1;
        for (int i = 0; i < t; i++) {
            if (a[i] <= b[i])
                max = std::max(max, a[i]);
            else {
                sum1 += 1 / (a[i] - b[i]);
                sum0 += a[i] / (a[i] - b[i]);
            }
        }
        max = std::max(max, sum0 / sum1);
        f[mask] = max;
    }
    printf("%.10lf\n", f[(1 << n) - 1]);
    return 0;
}