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#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>

int main() {
    int n;
    int t;

    std::cin >> n >> t;

    std::vector<double> prob(n, 0);
    // std::vector<double> dp(n * (n + 1), 0);
    std::vector<double> dpPrev(n, 0);
    std::vector<double> dpNow(n, 0);
    for (int i = 0; i < n; ++i) {
        double p;
        std::cin >> p;
        prob[i] = p;
    }
    std::sort(prob.begin(), prob.end(), std::greater{});

    // dp[1*n + 0] = prob[0];
    dpNow[0] = prob[0];
    for (int i = 0; i < n; ++i) {
        // dp[0*n + i] = 1;
        dpPrev[i] = 1;
    }

    double best = 0;

    int j = 0;
    int k = (j + t + 2)/2;
    bool done = false;
    for (int u = 1; u < n + 1 && !done; ++u) {
        for (int i = 1; i < n; ++i) {
            // dp[u*n + i] = prob[i] * dp[(u - 1)*n + i - 1]
            //             + (1.0 - prob[i]) * dp[u*n + i - 1];
            dpNow[i] = prob[i] * dpPrev[i - 1]
                     + (1.0 - prob[i]) * dpNow[i - 1];
        }
        while (u == k) {
            best = std::max(best, dpNow[j]);
            ++j;
            k = (j + t + 2)/2;
            if (k >= n || j >= n) {
                done = true;
                break;
            }
        }
        dpPrev.swap(dpNow);
        dpNow[0] = 0;
    }

    /*
    double best = 0;
    for (int i = 0; (i + t + 2)/2 < n; ++i) {
        double maybe = dp[((i + t + 2)/2)*n + i];
        if (maybe > best) {
            best = maybe;
        }
    }
    */

    std::cout << std::fixed << std::setprecision(10) << best << std::endl;
}