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#include <bits/stdc++.h>

#define ll long long
#define ve vector
#define fi first
#define se second
#define ld double
#define all(x) x.begin(), x.end()

using namespace std;

const double PI = 4 * atan(1.);
typedef complex<double> cd;

const int LOG = 18;
const int N = 1 << LOG;
cd w[N + 5];
int rev[N + 5];

void initFFT()
{
    for (int i = 0; i < N; i++)
        w[i] = cd(cos(2 * PI * i / N), sin(2 * PI * i / N));

    int k = 0;
    rev[0] = 0;
    for (int mask = 1; mask < N; mask++)
    {
        if (mask >> (k + 1))
            k++; // k - the most significant bit of mask
        rev[mask] = rev[mask ^ (1 << k)] ^ (1 << (LOG - 1 - k));
    }
}

cd F[2][N];            // maintain two layers
void FFT(cd *A, int k) // n = (1 << k)
{
    int L = 1 << k;
    // rearrange coefficients
    for (int mask = 0; mask < L; mask++)
        F[0][rev[mask] >> (LOG - k)] = A[mask];
    int t = 0, nt = 1; // t - current, nt - new
    for (int lvl = 0; lvl < k; lvl++)
    {
        int len = 1 << lvl;
        for (int st = 0; st < L; st += (len << 1))
            for (int i = 0; i < len; i++)
            {
                cd summand = F[t][st + len + i] * w[i << (LOG - 1 - lvl)];
                F[nt][st + i] = F[t][st + i] + summand;
                F[nt][st + len + i] = F[t][st + i] - summand;
            }
        swap(t, nt); // change layers
    }
    for (int i = 0; i < L; i++)
        A[i] = F[t][i];
}

vector<ld> multiply(vector<ld> A, vector<ld> B)
{
    int sz1 = (int)A.size(), sz2 = (int)B.size();
    int k = 0;
    // deg(A) = sz1 - 1, deg(B) = sz2 - 1, deg(AB) = sz1 + sz2 - 2
    while ((1 << k) < (sz1 + sz2 - 1))
        k++;
    int L = 1 << k;
    cd C[L], D[L];
    for (int i = 0; i < L; i++)
        C[i] = D[i] = 0;
    for (int i = 0; i < sz1; i++)
        C[i] = A[i];
    for (int i = 0; i < sz2; i++)
        D[i] = B[i];
    FFT(C, k);
    FFT(D, k);
    for (int i = 0; i < L; i++)
        C[i] *= D[i];
    FFT(C, k);
    reverse(C + 1, C + L);
    vector<ld> res;
    res.resize(sz1 + sz2 - 1);
    for (int i = 0; i < sz1 + sz2 - 1; i++)
        res[i] = ((ld)(C[i].real)() / L);
    return res;
}

ve<ld> calc(const ve<ld> &v)
{
    ve<ve<ld>> anses(v.size());
    for (int i = 0; i < v.size(); i++)
        anses[i] = {1. - v[i], 0, v[i]};
    ve<ve<ld>> nv;
    while (anses.size() > 1)
    {
        for (int i = 0; i + 1 < anses.size(); i += 2)
            nv.push_back(multiply(anses[i], anses[i + 1]));
        if (anses.size() & 1)
            nv.push_back(anses.back());
        nv.swap(anses);
        nv.clear();
    }
    return anses[0];
}

ve<ld> calced[N];

ld calc_helper(const ve<ld> &v, int n, int t)
{
    ve<ld> ans;
    if (calced[n].size())
    {
        ans = calced[n];
    }
    else
    {
        bool ok = 0;
        for (int i = n - 1; i > 0; i--)
        {
            if (calced[i].size())
            {
                ve<ld> cur(v.begin() + i, v.begin() + n);
                ok = 1;
                ans = multiply(calc(cur), calced[i]);
                break;
            }
        }
        if (!ok)
        {
            ve<ld> cur(v.begin(), v.begin() + n);
            ans = calc(cur);
        }
    }
    ld res = 0;
    for (int i = n + t; i < ans.size(); i++)
        res += ans[i];
    return res;
}

void solve()
{
    int n = 50000, t = 30;
    cin >> n >> t;
    ve<ld> v(n);
    for (int i = 0; i < n; i++)
    {
        //        v[i] = (ld)rand()/RAND_MAX;
        cin >> v[i];
    }
    sort(all(v), greater<ld>());
    int l = 1, r = n / 2;
    //    return;
    while (r - l + 1 > 2)
    {
        int sz = (r - l + 1) / 3;
        int m1 = l + sz;
        int m2 = r - sz;
        if (calc_helper(v, 2 * m1, t) < calc_helper(v, 2 * m2, t))
            l = m1;
        else
            r = m2;
    }
    ld ans = 0;
    for (int i = l; i <= r; i++)
        ans = max(ans, calc_helper(v, 2 * i, t));
    l = 1, r = n / 2;
    while (r - l + 1 > 2)
    {
        int sz = (r - l + 1) / 3;
        int m1 = l + sz;
        int m2 = r - sz;
        if (calc_helper(v, 2 * m1 + 1, t) < calc_helper(v, 2 * m2 + 1, t))
            l = m1;
        else
            r = m2;
    }
    for (int i = l; i <= r; i++)
        ans = max(ans, calc_helper(v, 2 * i + 1, t));

    cout << fixed << setprecision(7) << ans << "\n";
}

signed main()
{
    initFFT();
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int T = 1;
    //    cin >> T;
    while (T--)
        solve();
}