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#include <iostream>
#include <algorithm>
#include <iomanip>

using namespace std;

const int NMAX = 50007;

pair<double, double> p[NMAX];
double dp[NMAX];

double sum(int n, int k){
    double curr_sum = 0;
    double final_sum = 0;
    if(k > 0){
        for(int i=0;i<n;i++){
            dp[i] = p[i].second;
            curr_sum += p[i].second;
        }
        final_sum += curr_sum;
    }

    for(int i=1;i<k;i++){
        double temp_sum = 0;
        for(int j=0;j<n;j++){
            curr_sum -= dp[j];
            dp[j] = p[j].second * curr_sum;
            temp_sum += dp[j];
        }
        curr_sum = temp_sum;
        final_sum += curr_sum;
    }

    return final_sum;

}
int main(){

    int n, t;
    double q, answer = 0;

    cin>>n>>t;

    for(int i=0;i<n;i++){
        cin>>q;
        p[i] = {q, (1-q)/q};
    }

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

    double curr_p = 1;

    for(int i=0;i<t;i++){
        curr_p *= p[i].first;
    }
    answer = max(answer, curr_p);

    for(int i=t+1;i<n;i+=2){
        curr_p *= (p[i].first * p[i-1].first);
        if(p[i].first == 0){
            break;
        }
        double prob = curr_p * ((double)1 + sum(i+1, (i+1-t)/2));
        if(prob < answer){
            break;
        }
        answer = max(prob, answer);
    }

    cout<<fixed<<setprecision(10)<<answer;

    return 0;
}