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#include <bits/stdc++.h>

using namespace std;


const int N = 50004;
long double p[N];
long double left_dp[2*N], right_dp[2*N];

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

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

    if(t % 2 != n % 2) n--;

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

    int zero = n+2;

    for(int i = 0; i <= 2*zero; i++) {
        left_dp[i] = 0;
    }

    int start;
    if(t % 2 == 0) {
        start = 1;
        left_dp[zero] = 1;
    } 
    else {
        start = 2;
        left_dp[zero + 1] = p[1];
        left_dp[zero - 1] = 1 - p[1];
    }

    // cout << "n: " << n << "\n";
    // cout << "p[i]: ";
    // for(int i = 1; i <= n; i++) {
    //     cout << p[i] << " ";
    // }
    // cout << "start: " << start << "\n";

    long double best = 0;

    long double sum = 0;
        for(int pkt = zero+t; pkt <= zero+n; pkt += 2) {
            sum += left_dp[pkt];
        }

        best = max(best, sum);

    for(int x = start; x < n; x += 2) {
        long double p1 = p[x], p2 = p[x + 1];


        for(int pkt = zero-x-1; pkt <= zero+x+1; pkt += 2) {  // mozna zdoybc max x+1 pkt
            right_dp[pkt] = left_dp[pkt - 2]*p1*p2 + left_dp[pkt]*(p1+p2-2*p1*p2) + left_dp[pkt + 2]*(1-p1)*(1-p2);
        }

        for(int pkt = zero-x-1; pkt <= zero+x+1; pkt += 2) {
            left_dp[pkt] = right_dp[pkt];
        }   

        long double sum = 0;
        for(int pkt = zero+t; pkt <= zero+n; pkt += 2) {
            sum += left_dp[pkt];
        }

        best = max(best, sum);
    }

    cout << fixed << setprecision(20) << best << "\n";

    return 0;
}