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#include <bits/stdc++.h>
using namespace std;
#define fwd(i, a, n) for (int i = (a); i < (n); i++)
#define rep(i, n) fwd(i, 0, n)
#define all(X) X.begin(), X.end()
#define sz(X) int(size(X))
#define pb push_back
#define eb emplace_back
#define st first
#define nd second
using pii = pair<int, int>; using vi = vector<int>;
using ll = long long; using ld = long double;
#ifdef LOC
auto SS = signal(6, [](int) { *(int *)0 = 0; });
#define DTP(x, y) auto operator<<(auto &o, auto a) -> decltype(y, o) { o << "("; x; return o << ")"; }
auto operator<<(auto &o, auto a) -> decltype(all(a), o);
DTP(o << a.st << ", " << a.nd, a.nd);
DTP(for (auto i : a) o << i << ", ", all(a));
#define deb(x...) cerr << setw(4) << __LINE__ << ":[" #x "]: ", [](auto... arg_) { (( cerr << arg_ << ", " ), ...) << '\n'; }(x)
#else
#define deb(...) 0
#endif

typedef complex<double> C;
typedef vector<double> vd;
void fft(vector<C>& a) {
	int n = sz(a), L = 31 - __builtin_clz(n);
	static vector<complex<long double>> R(2, 1);
	static vector<C> rt(2, 1);  // (^ 10% faster if double)
	for (static int k = 2; k < n; k *= 2) {
		R.resize(n); rt.resize(n);
		auto x = polar(1.0L, acos(-1.0L) / k);
		fwd(i,k,2*k) rt[i] = R[i] = i&1 ? R[i/2] * x : R[i/2];
	}
	vi rev(n);
	rep(i,n) rev[i] = (rev[i / 2] | (i & 1) << L) / 2;
	rep(i,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 += 2 * k) rep(j,k) {
			// C z = rt[j+k] * a[i+j+k]; // (25% faster if hand-rolled)  /// include-line
			auto x = (double *)&rt[j+k], y = (double *)&a[i+j+k];        /// exclude-line
			C z(x[0]*y[0] - x[1]*y[1], x[0]*y[1] + x[1]*y[0]);           /// exclude-line
			a[i + j + k] = a[i + j] - z;
			a[i + j] += z;
		}
}
vd conv(const vd& a, const vd& b) {
	if (a.empty() || b.empty()) return {};
	vd res(sz(a) + sz(b) - 1);

    if (min(sz(a), sz(b)) <= 20) {
        rep(i, sz(a)) rep(j, sz(b))
            res[i + j] += a[i] * b[j];
        return res;
    }

	int L = 32 - __builtin_clz(sz(res)), n = 1 << L;
	vector<C> in(n), out(n);
	copy(all(a), begin(in));
	rep(i,sz(b)) in[i].imag(b[i]);
	fft(in);
	for (C& x : in) x *= x;
	rep(i,n) out[i] = in[-i & (n - 1)] - conj(in[i]);
	fft(out);
	rep(i,sz(res)) res[i] = imag(out[i]) / (4 * n);
	return res;
}

double atLeast(vector<double> questions, int t) {
    assert(sz(questions));
    auto rec = [&](auto _rec, int l, int r) -> vector<double> {
        if (l == r) {
            return {1 - questions[l], questions[l]};
        }
        int mid = (l + r) / 2;

        return conv(
            _rec(_rec, l, mid),
            _rec(_rec, mid+1, r)
        );
    };
    int qs = sz(questions);
    questions = rec(rec, 0, qs - 1);
    double ans = 0;
    rep(i, sz(questions)) {
        if (i - (qs - i) >= t)
            ans += questions[i];
    }
    return ans;
}

double brute(vector<double> questions, int t) {
    sort(questions.rbegin(), questions.rend());

    double best = 0;
    vector<double> dp = {1};
    for (auto q : questions) {
        dp.pb(0);

        double here = 0;
        for (int i = sz(dp) - 1; i >= 0; --i) {
            dp[i] = (1-q) * dp[i] + q * (i ? dp[i-1] : 0);

            int nok = sz(dp)-1 - i;
            if (i - nok >= t) here += dp[i];
        }

        best = max(best, here);
    }
    return best;
}

void solve() {
    int n, t;
    #ifdef CHECK
    n = 50000; t = 12800;
    #else
    cin >> n >> t;
    #endif

    vector<double> questions(n);
    #ifdef CHECK
    mt19937_64 rnd(chrono::high_resolution_clock().now().time_since_epoch().count());
    for (auto &q : questions) q = uniform_real_distribution()(rnd);
    #else
    for (auto &q : questions) cin >> q;
    #endif
    sort(questions.rbegin(), questions.rend());

    double best = 0;

    vector<double> big = {1}, prefbig = {1}, small = {1};
    for (auto q : questions) {
        if (sz(small) % 750 == 0) {
            big = conv(big, small);
            prefbig.resize(sz(big));
            prefbig.back() = big.back();
            for (int i = sz(big) - 2; i >= 0; --i)
                prefbig[i] = prefbig[i+1] + big[i];
            small = {1};
        }

        small.pb(0);
        for (int i = sz(small) - 1; i; --i)
            small[i] = small[i-1] * q + small[i] * (1 - q);
        small[0] *= 1 - q;

        int qSoFar = sz(small) + sz(big) - 2;

        if ((t + qSoFar) % 2)
            continue;
        if (qSoFar < t)
            continue;

        int hasToAnswer = (t + qSoFar) / 2;

        double here = 0;
        rep(ansSmall, sz(small)) {
            int ansBig = hasToAnswer - ansSmall;
            if (ansBig < 0) ansBig = 0;
            if (ansBig >= sz(big)) continue;
            here += small[ansSmall] * prefbig[ansBig];
        }

        best = max(best, here);
    }

    #ifdef LOC
    if (n < 1000) {
        double br = brute(questions, t);
        if (abs(br - best) > 1e-7) {
            deb(n, t);
            deb(questions);
            deb(br, best);
            assert(false);
        }
    }
    #endif

    cout << best << '\n';
}

int32_t main() {
    cin.tie(0)->sync_with_stdio(0);
    cout << fixed << setprecision(10);

    int z = 1;
    // cin >> z;
    rep(_, z) solve();

    cout << flush;
    _Exit(0);
}