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#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,abm,mmx,tune=native")
//#pragma clang diagnostic ignored "-Wunused-const-variable"
#include<vector>
#include<iostream>
#include<stack>
#include<cmath>
#include<algorithm>
#include<set>
#include<map>
#include<string>
#include<tuple>
#include<bitset>
#include<queue>
#include<unordered_map>
#include<unordered_set>
#include<random>
#include<assert.h>
#include<ctime>
#include <cassert>
#include <thread>
#include <mutex>
#include <semaphore>
#include <chrono>
//#define int long long
#define all(a) a.begin(), a.end()
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
using namespace std;
ll gcd(ll i, ll j) {
	if (i < j)swap(i, j);
	if (j == 0)return i;
	else return gcd(j, i % j);
}
#ifdef _MY
ll __builtin_popcount(ll x) { return x ? (__builtin_popcount(x >> 1) + (x & 1)) : 0; }
#endif
template<typename T> inline T getint() {
	T val = 0;
	char c;

	bool neg = false;
	while ((c = getchar()) && !(c >= '0' && c <= '9')) {
		neg |= c == '-';
	}

	do {
		val = (val * 10) + c - '0';
	} while ((c = getchar()) && (c >= '0' && c <= '9'));

	return val * (neg ? -1 : 1);
}
const ll INF = 1e7 + 100;
const int mod = 998244353, mod1 = 1000000007;
const ld eps = 1e-7, pi = acos(-1);
const int maxT = 503, maxN = 100'100, A = 311;
ll bp(ll et, ll b) {
	ll res = 1;
	for (int i = 30; i >= 0; --i) {
		res = (res * res) % mod;
		if ((b & (1 << i)) != 0)res = (res * et) % mod;
	}
	return res;
}
mt19937 mt_rand(time(0));
void panic() {
	cout << "No\n";
	exit(0);
}
ld get_time() {
	ll tmr = clock();
	return (ld)tmr / CLOCKS_PER_SEC;
}
int pl(int a, int b) {
	a += b;
	if (a >= mod)
		a -= mod;
	return a;
}
int mul(ll a, ll b) {
	return a * b % mod;
}

double dp[2][maxN];
void solve() {
	int n, t;
	cin >> n >> t;
	vector<double>p(n);
	for (auto& x : p) {
		//x = (double)(mt_rand() % 1'000'000) / 1'000'000;
		cin >> x;
	}
	sort(p.rbegin(), p.rend());
	const ll K = 1000;
	dp[0][0] = 1;
	double ans = 0;
	int l = 0, r = 1;
	for (int i = 0; i < n; ++i) {
		vector<double>pp = { p[i],1 - p[i] };
		double mx = 0;
		int ps = l - 1;
		int i1 = i % 2;
		int i2 = i1 ^ 1;
		for (int j = l; j < r; ++j) {
			for (int k = 0; k < pp.size(); ++k) {
				dp[i2][j + k] += dp[i1][j] * pp[k];
				if (dp[i2][j + k] > mx) {
					mx = dp[i2][j + k];
					ps = j + k;
				}
			}
			dp[i1][j] = 0;
		}
		int l1 = max(0LL, ps - K);
		int r1 = min(ps + K, (ll)n + 1);
		double tans = 0;
		const int can_do_err = i + 1 >= t ? (i + 1 - t) / 2 : -1;
		for (int t = l; t < r + 2; ++t) {
			if (t < l1 || t >= r1) {
				dp[i2][t] = 0;
			}
			else {
				if (t <= can_do_err) {
					tans += dp[i2][t];
				}
			}
		}
		l = l1;
		r = r1;
		ans = max(ans, tans);
	}
	cout << fixed << ans << "\n";

}
int32_t main()
{
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	cout.precision(14);
#ifdef _MY
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);


	/*time_t start, end;
	time(&start);*/
#else
	//freopen("epic.in", "r", stdin); freopen("epic.out", "w", stdout);
#endif
   // init();
	int t = 1;
	//cin >> t;
	while (t--) {
		solve();
	}
#ifdef _MY
	cout << "Time taken is : " << fixed << get_time() << " sec " << "\n";
#endif
	return 0;
}