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#include <bits/stdc++.h>

using namespace std;


#define _DEBUG
#ifdef _DEBUG
template<typename T1, typename T2> auto& operator<<(ostream& o, pair<T1, T2> a) { return o << "(" << a.first << ", " << a.second << ")"; }
template<typename T, typename OS> auto& operator<<(OS& o, T a) { o << "{"; for (auto b : a) o << b << ", "; return o << "}"; }
#define dbg(x...) cerr << "[" #x "]: ", [](auto... args) { ((cerr << args << ", "),...) << "\n"; }(x)
#else
#define dbg(...)
#endif

#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define F first
#define S second

using ll = long long;
using ld = double;
using pll = pair<ll,ll>;
using vi = vector<int>;

int main() {
    cin.tie(0)->sync_with_stdio(0);

    ll n, t;
    cin >> n >> t;
    vector<ld> v(n);
    for(ll i = 0 ; i < n ; ++i) cin >> v[i];
    sort(all(v), greater<>());
    ll m = (n+t)/2 + 2;
    m = min(m, n);
    vector<ld> dp(m+2);
    dp[0] = 1-v[0];
    dp[1] = 1;
    ld ans = 0;
    ll tr = sqrt(n);
    ll ti = 1;
    if(t == 0) ans = 1;
    if(t == 1) ans = v[0];
    for(ll i = 1 ; i < n ; ++i) {
        ti = max(ti, i/2-tr);
        while(ti < i-1 && dp[ti] < 1e-9) ti++;
        for(ll j = min(m, i) ; j >= ti ; --j) {
            dp[j] = dp[j]*(1-v[i]) + dp[j-1]*v[i];
        }
        if(i+1 <= m)
            dp[i+1] = 1;
        dp[0] = dp[0]*(1-v[i]);

        if(i+1 >= t)
            ans = max(ans, 1 - dp[(i+t)/2]);
    }
    cout << std::fixed << std::setprecision(7) << ans << '\n';

    return 0;
}