#include <bits/stdc++.h>

int n;
int w[22];
double f[1 << 22], a[22], b[22];

double work(int mask) {
    int t = 0;
    for (int i = 0; i < n; i++)
        if (mask >> i & 1) {
            a[t] = w[i];
            b[t] = f[mask ^ (1 << i)];
            t++;
        }
    if (a[0] <= b[0]) return a[0];
    double sump = 0, k = 1 / (a[0] - b[0]);
    for (int i = 1; i < t; i++) {
        double del = (a[i - 1] - a[i]) * k;
        if (sump + del > 1) return a[i - 1] - (1 - sump) / k;
        sump += del;
        k += 1 / (a[i] - b[i]);
    }
    return a[t - 1] - (1 - sump) / k;
}

int main() {
    scanf("%d", &n);
    for (int i = 0; i < n; i++) scanf("%d", &w[i]);
    std::sort(w, w + n, [](int x, int y) { return x > y; });
    for (int mask = 1; mask < 1 << n; mask++) f[mask] = work(mask);
    printf("%.10lf\n", f[(1 << n) - 1]);
    return 0;
}