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#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;

#define FOR(x, b, e) for(int x = (b); x <= (e); ++(x))
#define FORD(x, b, e) for(int x = (b); x >= (e); --(x))
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define ALL(c) (c).begin(), (c).end()
#define SIZE(x) ((int)(x).size())
#define FOREACH(a, b) for (auto&a : (b))
#define PB push_back
#define PF push_front
#define ST first
#define ND second
#define DBG(vari) cerr<<#vari<<" = "<<(vari)<<endl

template <typename T>
std::ostream& operator<<(std::ostream &output, const vector<T> &vec)
{
    output << "[";
    FOREACH(x, vec) output << x << ", ";
    output << "]";
    return output;
}

template <typename T, typename U>
std::ostream& operator<<(std::ostream &output, const pair<T,U> &p)
{
    output << "(";
    output << p.ST << ", " << p.ND;
    output << ")";
    return output;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  int n, T; cin >> n >> T;
  vector<double> p(n); REP(i, n) cin >> p[i];
  sort(ALL(p));
  reverse(ALL(p));

  vector<vector<double>> P(2);
  REP(i, 2) P[i].resize(n+1, 0);

  P[0][0] = 1.0;
  FOR(k, 1, n) {
    P[0][k] = P[0][k-1] * (1-p[k-1]); 
  }

  vector<double> wyn(n+1, 0);

  const double eps = 1e-20;

  FOR(t, 1, n) {
    P[t%2][t-1] = 0.0;

    FOR(k, t, n) {
      {

        if (P[t%2][k-1] < eps && P[(t-1)%2][k-1] < eps)  {
          P[t%2][k] = 0.0;
        }
        else
        P[t%2][k] = P[t%2][k-1] * (1-p[k-1]) + P[(t-1)%2][k-1] * (p[k-1]); 

        if (t - (k-t) >= T)
          wyn[k] += P[t%2][k];
      }
    }

  }
  
  double w = 0.0;
  FOR(k, 0, n) {
    w = max(w, wyn[k]);
  }

  cout << std::fixed << std::setprecision(7) << w << endl;

}