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#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
#define deb(...)
#define DBP(...)
using namespace std;
using   ll         = long long;
using   vi         = vector<int>;
using   pii        = pair<int, int>;
#define pb           push_back
#define mp           make_pair
#define x            first
#define y            second
#define rep(i, b, e) for (int i = (b); i < (e); i++)
#define each(a, x)   for (auto& a : (x))
#define all(x)       (x).begin(), (x).end()
#define sz(x)        int((x).size())

void run();

int main() {
	cin.sync_with_stdio(0); cin.tie(0);
	cout << fixed << setprecision(12);
	run();
	cout << flush; _Exit(0);
}

using dbl = long double;
using cmpl = complex<dbl>;

void fft(vector<cmpl>& a) {
	static vector<cmpl> w(2, 1);
	int n = sz(a);

	for (int k = sz(w); k < n; k *= 2) {
		w.resize(n);
		rep(i, 0, k) w[k+i] = exp(cmpl(0, M_PI*i/k));
	}

	vi rev(n);
	rep(i, 0, n) rev[i] = (rev[i/2] | i%2*n) / 2;
	rep(i, 0, n) if (i < rev[i]) swap(a[i], a[rev[i]]);

	for (int k = 1; k < n; k *= 2) {
		for (int i = 0; i < n; i += k*2) rep(j, 0, k) {
			auto d = a[i+j+k] * w[j+k];
			a[i+j+k] = a[i+j] - d;
			a[i+j] += d;
		}
	}
}

vector<dbl> convolve(const vector<dbl>& a, const vector<dbl>& b) {
	if (a.empty() || b.empty()) return {};
	int len = sz(a)+sz(b)-1, n = 1;
	while (n < len) n *= 2;

	vector<cmpl> in(n), out(n);
	rep(i, 0, sz(a)) in[i].real(a[i]);
	rep(i, 0, sz(b)) in[i].imag(b[i]);

	fft(in);
	each(x, in) x *= x;
	rep(i, 0, n) out[i] = in[-i&(n-1)] - conj(in[i]);
	fft(out);

	vector<dbl> ret(len);
	rep(i, 0, len) ret[i] = imag(out[i]) / (n*4);
	return ret;
}

vector<dbl> prob;
int t;
dbl ans;

vector<dbl> solve(int begin, int end, vector<dbl> pref, int offset) {
	if (end-begin <= 0) return {1};

	int k = (t+end+1) / 2 - offset;

	if (end-begin == 1) {
		dbl p = prob[begin];
		if (k-1 < sz(pref)) {
			dbl alt = pref[k-1] * p;
			rep(i, k, sz(pref)) alt += pref[i];
			ans = max(ans, alt);
		}
		return {1-p, p};
	}

	int endK = min(k+1, sz(pref));
	int beginK = clamp(k-(end-begin), 0, endK);

	rep(i, endK, sz(pref)) pref[endK-1] += pref[i];
	pref.resize(endK);
	pref.erase(pref.begin(), pref.begin()+beginK);
	offset += beginK;

	int mid = (begin+end) / 2;
	vector<dbl> L = solve(begin, mid, pref, offset);
	pref = convolve(pref, L);
	vector<dbl> R = solve(mid, end, std::move(pref), offset);
	return convolve(L, R);
}

void run() {
	int n;
	cin >> n >> t;

	prob.resize(n);
	each(e, prob) cin >> e;
	sort(all(prob), greater<dbl>());

	ans = 0;
	solve(0, n, {1}, 0);
	cout << ans << '\n';
}