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#include <cstdio>
#include <cstdlib>
#include <cassert>

#include <array>
#include <iterator>
#include <algorithm>

double data[50000];

double compute_prob(int i, int remaining, int n) {
    if (i == n) {
        return 1.0;
    }
    double p = data[i] * compute_prob(i + 1, remaining - 1, n);
    if (i + remaining + 2 <= n) {
        p += (1.0 - data[i]) * compute_prob(i + 1, remaining + 1, n);
    }
    return p;
}

int main() {
    int n, t;
    scanf("%d %d\n", &n, &t);

    for (int i = 0; i < n; i++) {
        scanf("%lf\n", &data[i]);
    }

    std::sort(std::rbegin(data), std::rend(data));

    double best = 0.0;
    for (int i = t; i < n; i++) {
        best = std::max(best, compute_prob(0, t, i));
    }

    printf("%.8lf\n", best);

    return 0;
}