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#include "bits/stdc++.h"
using namespace std;

#define rep(i, b, e) for(int i = (b); i <= (e); i++)
#define per(i, b, e) for(int i = (e); i >= (b); i--)
#define FOR(i, b, e) rep(i, b, (e) - 1)
#define SZ(x) int(x.size())
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define st first
#define nd second
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;

auto &operator<<(auto &o, pair<auto, auto> p) {
    return o << "(" << p.st << ", " << p.nd << ")"; }
auto operator<<(auto &o, auto x)->decltype(end(x), o) {
    o << "{"; int i=0; for(auto e: x) o << ", " + 2*!i++ << e;
    return o << "}"; }
#ifdef LOCAL
#define deb(x...) cerr << "[" #x "]: ", [](auto...$) { \
    ((cerr << $ << "; "),...) << endl; }(x)
#else
#define deb(...)
#endif

using D = long double;
const int N = 50'010;

D dp[N];

void solve() {
    int n, t;
    cin >> n >> t;
    vector<D> p(n);
    for(auto &x: p) cin >> x;
    sort(all(p)), reverse(all(p));
    D ans = 0;
    const D EPS = D(1e-9) / N;
    dp[1] = 1;
    int l = 1, r = 1;
    FOR(j, 0, n) {
        auto &x = p[j];
        for(int i = ++r; i >= l; i--) {
            dp[i] = (1 - x) * dp[i] + x * dp[i - 1];
        }
        while(dp[l] < EPS) dp[l++] = 0;
        while(dp[r] < EPS) dp[r--] = 0;
        D sum = 0;
        for(int i = max(l, (t + j) / 2 + 2); i <= r; i++) {
            sum += dp[i];
        }
        ans = max(ans, sum);
    }
    cout << fixed << setprecision(7);
    cout << ans << '\n';
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    int tt = 1;
    // cin >> tt;
    FOR(te, 0, tt) solve();
    return 0;
}