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#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimization ("unroll-loops")

using namespace std;

double p[50001];
double p1[50001];
double dp[2][50001];

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

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

    cout << fixed << setprecision(7);

    for (int i = 1; i <= n; ++i)
    {
        cin >> p[i];
    }

    sort(p + 1, p + n + 1, greater<>());

    for (int i = 1; i <= n; ++i) p1[i] = 1 - p[i];

    dp[0][0] = 1;
    double best = 0;
    double lastBest = 0;
    double eps = 0.00000001;
    int c = 1;

    for (int i = 1; i <= n; ++i)
    {
        double sum = 0;
        int required = (i + t + 1) / 2;

        if (i < t || (((i + t) & 1) && i != n))
        {
            dp[c][0] = dp[c ^ 1][0] * (1 - p[i]);
            for (int j = 1; j <= i; ++j)
            {
                dp[c][j] = dp[c ^ 1][j - 1] * p[i] + dp[c ^ 1][j] * p1[i];
            }
        }
        else
        {
            dp[c][0] = dp[c ^ 1][0] * (1 - p[i]);
            for (int j = 1; j < required; ++j)
            {
                dp[c][j] = dp[c ^ 1][j - 1] * p[i] + dp[c ^ 1][j] * p1[i];
            }
            for (int j = required; j <= i; ++j)
            {
                dp[c][j] = dp[c ^ 1][j - 1] * p[i] + dp[c ^ 1][j] * p1[i];
                sum += dp[c][j];
            }
        
            best = max(best, sum);

            lastBest = best;

            if (best + eps >= 1) break;
        }

        c ^= 1;
    }

    cout << best << '\n';
}