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/// UH Top
#include <bits/stdc++.h>
#define db(x)   cerr << #x << ':' << (x) << '\n';
#define all(v)  (v).begin(), (v).end()
#define allr(v) (v).rbegin(), (v).rend()
// #define int     ll
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
// typedef __int128_t int128;
typedef pair<ll, ll> pii;
typedef pair<ld, ll> pdi;
typedef pair<ld, ld> pdd;
typedef pair<ld, pdd> pdp;
typedef pair<string, ll> psi;
typedef pair<ll, string> pls;
typedef pair<string, string> pss;
typedef pair<ll, pii> pip;
typedef pair<pii, pii> ppp;
// typedef complex<ld> point;
// typedef vector<point> polygon;
typedef vector<ll> vi;
// typedef pair<point, int> ppi;
#define prec(n)                                                                \
	cout.precision(n);                                                         \
	cout << fixed
const ll mod = (1e9 + 7);
const ld eps = (1e-9);
const ll oo = (ll)(1e9 + 5);
#define pi   acos(-1)
#define MAXN (ll)(4e2 + 5)

struct point {
	double x, y;
	point(double x = 0, double y = 0) : x(x), y(y) {}
};

point operator+(const point &a, const point &b) {
	return {a.x + b.x, a.y + b.y};
}
point operator-(const point &a, const point &b) {
	return {a.x - b.x, a.y - b.y};
}
point operator*(const point &a, const point &b) {
	return {a.x * b.x - a.y * b.y, a.x * b.y + a.y * b.x};
}
point operator/(const point &a, double d) { return {a.x / d, a.y / d}; }

void fft(vector<point> &a, int sign = 1) {
	int n = a.size(); // n should be a power of two
	double theta = 8 * sign * atan(1.0) / n;
	for (int i = 0, j = 1; j < n - 1; ++j) {
		for (int k = n >> 1; k > (i ^= k); k >>= 1)
			;
		if (j < i)
			swap(a[i], a[j]);
	}
	for (int m, mh = 1; (m = mh << 1) <= n; mh = m) {
		int irev = 0;
		for (int i = 0; i < n; i += m) {
			point w = point(cos(theta * irev), sin(theta * irev));
			for (int k = n >> 2; k > (irev ^= k); k >>= 1)
				;
			for (int j = i; j < mh + i; ++j) {
				int k = j + mh;
				point x = a[j] - a[k];
				a[j] = a[j] + a[k];
				a[k] = w * x;
			}
		}
	}
	if (sign == -1)
		for (auto &p : a)
			p = p / n;
}

vector<point> convolve(vector<point> &a, vector<point> &b) {
	int n = a.size();
	int m = b.size();
	int sum = n + m;
	while (sum != (sum & -sum))
		sum += (sum & -sum);
	while (a.size() < sum)
		a.push_back(point(0, 0));
	while (b.size() < sum)
		b.push_back(point(0, 0));

	fft(a, 1);
	fft(b, 1);

	vector<point> res(sum);
	for (int i = 0; i < sum; i++)
		res[i] = a[i] * b[i];

	fft(res, -1);

	return res;
}

vector<point> convolve_vectors(vector<vector<point>> &v) {
	if (v.size() == 1)
		return v[0];
	vector<vector<point>> m[2];
	for (int i = 0; i < v.size(); i++) {
		m[i & 1].push_back(v[i]);
	}
	auto a = convolve_vectors(m[0]);
	auto b = convolve_vectors(m[1]);
	return convolve(a, b);
}

double aux(vector<double> &p, int x, int t) {
	vector<vector<point>> to_conv(x);
	for (int i = 0; i < x; i++) {
		to_conv[i] = {point(1 - p[i], 0), point(p[i], 0)};
	}

	auto conv = convolve_vectors(to_conv);
	double ans = 0;
	for (int i = 0; i <= x; i++) {
		if (i - (x - i) >= t) {
			ans += conv[i].x;
		}
	}

	return ans;
}

int32_t main() {
	ios_base::sync_with_stdio(0);
	cin.tie(0);

	int n, t;
	cin >> n >> t;
	vector<double> p(n);
	for (auto &x : p)
		cin >> x;

	sort(allr(p));

	int ans = t;
	for (int i = (1 << 15); i; i >>= 1) {
		if (ans + i > n)
			continue;
		int x1 = ans + i - 1;
		int x2 = ans + i;
		double v1 = aux(p, x1, t);
		double v2 = aux(p, x2, t);
		// cout << x1 << ' ' << v1 << '\n';
		// cout << x2 << ' ' << v2 << '\n';
		if (v2 > v1 + eps) {
			ans += i;
		}
	}

	prec(15);

	// cout << ans << '\n';
	cout << aux(p, ans, t) << '\n';

	return 0;
}