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#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    int n, t;
    cin >> n >> t;
    
    vector<double> p(n);
    for (int i = 0; i < n; i++) {
        cin >> p[i];
    }
    
    sort(p.begin(), p.end(), greater<double>());
    
    vector<double> dp(2 * n + 1, 0.0);
    dp[n] = 1.0; 
    
    double best_prob = 0.0;
    for (int k = 0; k < n; k++) {
        vector<double> new_dp(2 * n + 1, 0.0);
        for (int s = 0; s <= 2 * n; s++) {
            if (dp[s] > 0) {
                new_dp[s + 1] += dp[s] * p[k];    
                new_dp[s - 1] += dp[s] * (1 - p[k]);
            }
        }
        dp = new_dp;
        
        
        double prob = 0.0;
        for (int s = t + n; s <= 2 * n; s++) {
            prob += dp[s];
        }
        best_prob = max(best_prob, prob);
        
        
        if (k == 3) break; 
    }
    
    cout.precision(7); 
    cout << fixed << best_prob << "\n";
    
    return 0;
}