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

using namespace std;

using ld = long double;

ld success[50500];
vector<double> tests;

inline bool relevant(int n, ld val) {
	return val * n * n * 1000000 >= 1;
}

int main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int n, t;
	cin >> n >> t;
	ld k;
	for(int i = 0; i < n; i++) {
		cin >> k;
		tests.push_back(-k);
	}
	int relevant_begin = 0, relevant_end = 1; 
	sort(tests.begin(), tests.end());
	for(int i = 0; i < n; i++) {
		tests[i] = -tests[i];
	}
	success[0] = 1;
	ld best = 0;
	for(int i = 0; i < n; i++) {
		ld res = 0;
		for(int j = relevant_end - 1; j >= relevant_begin; j--) {
			success[j + 1] += success[j] * tests[i];
			success[j] *= 1 - tests[i];
		}
		if (relevant(n, success[relevant_end])) {
			relevant_end++;
		}
		while(!relevant(n, success[relevant_begin])) {
			relevant_begin++;
		}
		for(int j = relevant_begin; j < relevant_end; j++) {
			if (j - (i + 1 - j) >= t) {
				res += success[j];
			}
		}
		best = max(best, res);
	}
	cout << setprecision(15) << fixed << best << "\n";
}