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#include <cstdio>
#include <vector>
#include <algorithm>
#include <unordered_map>

using namespace std;

int main()
{
    int n, t;
    vector<double> P;

    scanf("%d%d", &n, &t);
    P.resize(n);
    for (int i = 0; i < n; i++)
        scanf("%lf", &P[i]);
    sort(P.begin(), P.end(), greater<double>());

    double best = 0.0;

    unordered_map<int, double> prev;

    prev[0] = 1.0;

    for (int i = 0; i < n; i++)
    {
        unordered_map<int, double> next;

        for (int j = -(i + 1); j <= i + 1; j += 2)
            next[j] = prev[j - 1] * P[i] + prev[j + 1] * (1 - P[i]);
        
        double current = 0.0;
        for (int j = t; j <= i + 1; j++)
            current += next[j];

        if (current > best)
            best = current;

        swap(prev, next);
    }

    printf("%.9lf\n", best);


    return 0;
}