#include <bits/stdc++.h>
using namespace std;

const int MAXN = 5050;

int n, k; double a[MAXN];
double dp[2][2 * MAXN];
int main() {
	cin.tie(0); ios_base::sync_with_stdio(0);
	cin >> n >> k;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
	}
	
	sort(a + 1, a + 1 + n, greater<double>());
	dp[0][MAXN] = 1;
	double ans = 0;
	for (int i = 1; i <= n; i++) {
		for (int j = 0; j < 2 * MAXN; j++)
			dp[i & 1][j] = 0;
		
		for (int j = MAXN - i; j <= MAXN + i; j++) {
			dp[i & 1][j] = dp[~i & 1][j - 1] * a[i] + dp[~i & 1][j + 1] * (1 - a[i]);
		}
		double s = 0;
		for (int j = MAXN + k; j < 2 * MAXN; j++) {
			s += dp[i & 1][j];
		}
		ans = max(ans, s);
	}
	cout.precision(10);
	cout << fixed << ans;
}