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#include <bits/stdc++.h>
using namespace std;
#define st first
#define nd second
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define BOOST ios_base::sync_with_stdio(0), cin.tie(0)
typedef long long ll;
typedef long double ld;
typedef pair<int, int> ii;

const int N = 1e5 + 5, s = 5e4;
const ld eps = 1e-15;
ld d[N];
ld tmp[N];

int main(){
	BOOST;
	int n, bar;
	cin >> n >> bar;
	vector<ld> p(n);
	for(int i=0; i<n; i++){
		cin >> p[i];
	}
	sort(all(p), greater<ld>());
	int l = s, r = s;
	d[s] = 1;
	bar += s;
	ld ans = 0;
	// int sdst = 0;
	for(int i=0; i<n; i++){
		if(r < l) break;

		// printf("lr = [%d, %d]\n", l, r);
		// sdst = max(sdst, r-l);

		l--, r++;
		for(int j=l; j<=r; j++) tmp[j] = d[j-1] * p[i] + d[j+1] * (1-p[i]);
		for(int j=l; j<=r; j++) d[j] = tmp[j];
		while(l <= r && d[l] < eps){
			d[l] = 0;
			l++;
		}
		while(l <= r && d[r] < eps){
			d[r] = 0;
			r--;
		}

		// cout << "dist:\n";
		// for(int j=l; j<=r; j++){
		// 	cout << fixed << setprecision(7) << "d[" << j-s << "]: " << d[j] << "\n";
		// }
		// cout << "\n";

		ld sum = 0;
		for(int j=max(l, bar); j<=r; j++) sum += d[j];
		ans = max(ans, sum);
	}

	// cout << "Dst = " << sdst << "\n";

	cout << fixed << setprecision(9) << ans << "\n";
}