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#include <bits/stdc++.h>
using ll = long long;
using sz = size_t;
using namespace std;

// make the code less c++-readable:
template<class T> using v = vector<T>; 
template<class T> using vv = v<v<T>>; 
using vi = v<int>; using vll = v<ll>; using vvi = vv<int>; using vvll = vv<ll>;

// hai loading utilities
#define $T template<class T>
#define $Ts template<class... T>
$T T Load() { T v; cin >> v; return v; }
$T auto Loads(int n) { v<T> v; v.reserve(n); while(n--) v.emplace_back(Load<T>()); return v; }
$T auto Loads() { return Loads<T>(Load<int>()); }
template<class T, int N> auto Loada() { array<T, N> a; for (T& v: a) v = Load<T>(); return a; }
$Ts auto Cols(int rows) { tuple<v<T>...> t; while(rows--) [&]<sz... I>(index_sequence<I...>){(std::get<I>(t).push_back(Load<T>()), ...);}(index_sequence_for<T...>{}); return t; }
//$Ts auto Rows(int rows) { v<tuple<T...>> v; while(rows--) { v.emplace_back(Load<T>()...); } return v; } bugged :(
struct _aIV { $T operator vector<T>() { return Loads<T>(n); } sz n; };
struct _aI { $T operator T() { return Load<T>(); } _aIV operator()(sz n) { return {n}; } }; static inline _aI $;  /* int N = $;  vi Y = $(N); */
#define MAKE_LOADER(T, alias) \
  T alias() { return Load<T>(); }   /* int x = Int(); */\
  auto alias##s() { return Loads<T>(); }   /* vector<> xs = Ints(); */\
  auto alias##s(int n) { return Loads<T>(n); }   /* vector<> xs = Ints(7); */\
  template<int N> auto alias##a() { return Loada<T, N>(); }   /* array<> xs = Inta<7>();  */\
// line intentionally left blank
MAKE_LOADER(int, Int)
MAKE_LOADER(long long, LL)
MAKE_LOADER(char, Char)
MAKE_LOADER(string, String)
// kthxbye


using Real = double;

void test() {    
    const int N = $;
    const int T = $;
    v<Real> szanse = $(N);
    sort(szanse.begin(), szanse.end(), greater<Real>{});
    
    vector<Real> rozkład(2*50'000 + 44, 0);
    Real* const R = rozkład.data() + rozkład.size() / 2;
    
    R[0] = 1;
    int mini = 0, maxi = 0;
    
    Real odp = 0;
    Real totalnie = 0;
    for (const Real sza : szanse) {
        
        Real bilans_totalności = 0;
        if ((T % 2) == (abs(mini) % 2)) {
            bilans_totalności -= R[T] * (1-sza);
            //assert(bilans_totalności <= 0);
        } else {
            bilans_totalności += R[T-1] * sza;
            //assert(bilans_totalności >= 0);
        }
        //cout << sza << ":" << bilans_totalności << "   ";
        
        for (int ile = mini; ile <= maxi; ile += 2) {
            R[ile-1] += R[ile] * (1-sza);
            R[ile+1] = R[ile] * sza;
        }
        --mini;
        ++maxi;
        
        constexpr static Real tol = 1e-15;   
        constexpr static sz limit = 1000;     
        
        if (R[mini] < tol && maxi - mini > limit+2) {
            R[mini+2] += R[mini];
            R[mini] = 0;
            mini += 2;
        }
        if (R[maxi] < tol && maxi - mini > limit) {
            R[maxi-2] += R[maxi];
            R[maxi] = 0;
            maxi -= 2;
        }
        
        totalnie += bilans_totalności;
        odp = max(odp, totalnie);
    }
    
    cout << fixed << setprecision(17) << odp << endl;
}

[[maybe_unused]] void jeden_test() { test(); }
[[maybe_unused]] void wiele_test() { int T = $; while (T--) test(); }

int main() {
    jeden_test();
    return 0;
}