#include <bits/stdc++.h>

using LD = long double;

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

LD work(int mask) {
    const int t = __builtin_popcount(mask);
    if (t <= 1) return 0;
    std::vector<LD> 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)]);
        }
    assert(a[0] > b[0]);
    LD sump = 0, k = 1 / (a[0] - b[0]);
    for (int i = 1; i < t; i++) {
        LD 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 = 0; mask < 1 << n; mask++) f[mask] = work(mask);
    printf("%.10Lf\n", f[(1 << n) - 1]);
    return 0;
}