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

typedef int64_t ll;
typedef uint64_t ull;
typedef unsigned int ui;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<long long> vll;
constexpr ll LINF = 1e18;
constexpr int INF = 1e9;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(18);

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

    vector<double> p(n);
    for (int i = 0; i < n; ++i) {
        cin >> p[i];
    }
    sort(p.begin(), p.end(), greater<double>());

    double dp[n + 1][n + 1];
    for (int i = 0; i <= n; ++i) {
        for (int j = 0; j <= n; ++j) {
            dp[i][j] = 0.0;
        }
    }

    dp[0][0] = 1.0;
    for (int i = 1; i <= n; ++i) {
        dp[i][0] = dp[i - 1][0] * (1 - p[i - 1]);
        for (int j = 1; j <= i; ++j) {
            dp[i][j] = dp[i - 1][j - 1] * p[i - 1] + dp[i - 1][j] * (1 - p[i - 1]);
        }
    }

    // for (int i = 0; i <= n; ++i) {
    //     for (int j = 0; j <= n; ++j) {
    //         cout << dp[i][j] << ' ';
    //     }
    //     cout << '\n';
    // }

    double best = 0;
    for (int i = t; i <= n; ++i) {
        int correct_to_pass = i - (i - t) / 2;

        double sum = 0;
        for (int j = correct_to_pass; j <= i; ++j) {
            sum += dp[i][j];
        }

        if (sum > best) {
            best = sum;
        }
    }

    cout << setprecision(18) << best << endl;

    return 0;
}