#include <bits/stdc++.h>
/*#include <iostream>
#include <climits>
#include <cstring>
#include <algorithm>
#include <queue>
#include <vector>
#include <bitset>
*/
using namespace  std;
#define  int long long
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef vector<int> vi;
#define fi first
#define se second
#define pb  push_back
#define inf 1ll<<62
#define db double
#define endl "\n"
//#define max(a,b) ((a)>(b)?(a):(b))
//#define min(a,b) ((a)<(b)?(a):(b))
#define de_bug(x) cerr << #x << "=" << x << endl
#define all(a) a.begin(),a.end()
#define IOS   std::ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define  fer(i,a,b)  for(int i=a;i<=b;i++)
#define  der(i,a,b)  for(int i=a;i>=b;i--)
const int mod = 1e9 + 7;
const int N = 5e3 + 10;
int n, m , k;
db g[N];
db f[N][2 * N];
db ans;
db a[N];
void solve() {
	cin >> n >> m;
	fer(i, 1, n)cin >> a[i];
	sort(a + 1, a + n + 1, greater<double>());
	f[0][n] = 1;
	double ans = 0;
	for(int i = 1; i <= n; i++) {
		for(int j = n - i + 1; j <= n + i - 1; j++) {
			f[i][j + 1] += f[i - 1][j] * a[i];
			f[i][j - 1] += f[i - 1][j] * (1 - a[i]);
		}
		for(int j = n + m; j <= n + i; j++)g[i] += f[i][j];
	}
	fer(i, 1, n) ans = max(ans, g[i]);
	cout << fixed << setprecision(10) << ans << endl;
}
signed main() {
	IOS;
	int _ = 1;
	//cin>>_;
	while( _-- )
		solve();
	return 0;
}