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

double solve(int n, int t, vector<double>& p) {
    sort(p.rbegin(), p.rend());

    double max_prob = 0.0;

    for (int k = t; k <= n; ++k) {
        int c = (t + k + 1) / 2;
        if (c > k) continue;

        vector<double> dp(c + 1, 0.0);
        dp[0] = 1.0;

        for (int i = 0; i < k; ++i) {
            double prob = p[i];
            for (int j = min(i + 1, c); j > 0; --j) {
                dp[j] = dp[j] * (1 - prob) + dp[j - 1] * prob;
            }
        }

        double sum = 0.0;
        for (int m = c; m <= k; ++m) {
            if (m <= c) sum += dp[m];
        }
        if (sum > max_prob) {
            max_prob = sum;
        }
    }

    return max_prob;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n, t;
    cin >> n >> t;

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

    cout << fixed << setprecision(20) << solve(n, t, p) << "\n";

    return 0;
}