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

typedef long double ld;

const int MAXN = 50 * 1000 + 17;
ld p[MAXN];
ld dp1[2 * MAXN];
ld dp2[2 * MAXN];

int main () {
    ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n, t;
    cin >> n >> t;

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

    sort(p, p + n);
    reverse(p, p + n);

    ld wyn = 0;
    //MAXN to 0 punktow
    dp1[MAXN] = 1;
    for (int i = 0; i < n; i ++) {
        for (int j = -(i + 1); j <= (i + 1); j ++) {
            dp2[j + MAXN] = dp1[j + MAXN - 1] * p[i] + dp1[j + MAXN + 1] * (ld(1) - p[i]);
        }

        ld aktwyn = 0;
        for (int j = MAXN + t; j <= MAXN + i + 1; j ++) {
            aktwyn += dp2[j];
        }
        wyn = max(wyn, aktwyn);
        swap(dp1, dp2);
    }

    cout << fixed << setprecision(18) << wyn << "\n";

    return 0;
}