#include <bits/stdc++.h>
using namespace std;

using i64 = long long;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    auto solve = [&]() {
        int n, k;
        cin >> n >> k;

        vector<double> p(n);
        for (int i = 0; i < n; i++) {
            cin >> p[i];
        }

        sort(p.rbegin(), p.rend());

        double ans = 0;
        vector<double> dp(2 * n + 1), ndp(dp);
        dp[n] = 1;

        for (int i = 0; i < n; i++) {
            fill(ndp.begin(), ndp.end(), 0);
            for (int x = 0; x <= 2 * n; x++) {
                if (dp[x] != 0) {
                    ndp[x - 1] += dp[x] * (1 - p[i]);
                    ndp[x + 1] += dp[x] * p[i];
                }
            }
            ans = max(ans, accumulate(ndp.begin() + n + k, ndp.end(), 0.0));
            swap(dp, ndp);
        }

        cout << fixed << setprecision(20) << ans << '\n';
    };
    
    solve();
    
    return 0;
}