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#include <bits/stdc++.h>

using namespace std;

typedef unsigned uint;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ldbl;
typedef pair<int, int> pii;
typedef pair<uint, uint> puu;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pull;
typedef pair<double, double> pdd;
typedef vector<int> vi;
typedef vector<uint> vu;
typedef vector<ll> vll;
typedef vector<ull> vull;
typedef vector<pii> vpii;
typedef vector<puu> vpuu;
typedef vector<pll> vpll;
typedef vector<pull> vpull;
typedef vector<string> vstr;
typedef vector<double> vdbl;
typedef vector<ldbl> vldbl;
#define pb push_back
#define ppb pop_back
#define pfr push_front
#define ppfr pop_front
#define emp emplace
#define empb emplace_back
#define be begin
#define rbe rbegin
#define all(x) (x).be(), (x).end()
#define rall(x) (x).rbe(), (x).rend()
#define fir first
#define sec second
#define mkp make_pair
#define brif(cond) if (cond) break
#define ctif(cond) if (cond) continue
#define retif(cond) if (cond) return
void fastio() {ios_base::sync_with_stdio(false);cin.tie(nullptr);}
template<typename T> T gcd(T a, T b) {return b ? gcd(b, a%b) : a;}
template<typename T> T extgcd(T a, T b, T &x, T &y)
{
    T x0 = 1, y0 = 0, x1 = 0, y1 = 1;
    while (b) {
        T q = a/b; a %= b; swap(a, b);
        x0 -= q*x1; swap(x0, x1);
        y0 -= q*y1; swap(y0, y1);
    }
    x = x0; y = y0; return a;
}
int ctz(uint x) {return __builtin_ctz(x);}
int ctzll(ull x) {return __builtin_ctzll(x);}
int clz(uint x) {return __builtin_clz(x);}
int clzll(ull x) {return __builtin_clzll(x);}
int popcnt(uint x) {return __builtin_popcount(x);}
int popcntll(ull x) {return __builtin_popcountll(x);}
int bsr(uint x) {return 31^clz(x);}
int bsrll(ull x) {return 63^clzll(x);}

#define N 50008

double p[N];
double f[N];

int main()
{
    fastio();

    int n, t;
    ///int base = 0;
    double ans = 0.0;

    cin >> n >> t;
    for (int i = 0; i < n; ++i) cin >> p[i];
    sort(p, p+n, greater<double>());
    while (n > 0 && p[n-1] == 0.0) --n;
    retif(n < t) cout << "0.0\n", 0;
    ///while (base < n && p[base] == 1.0) ++base;
    ///retif(base >= t) cout << "1.0\n", 0;

    //int opc = 0;
    f[0] = 1;
    for (int i = 0; i < n; ++i) {
        double np = 1.0-p[i];
        f[i+1] = f[i]*p[i];// opc += 1;
        for (int j = i; j > 0; --j) {
            f[j] = np*f[j]+p[i]*f[j-1];
            //opc += 3;
        }
        f[0] *= np;// opc += 1;
        if (i+1 >= t && (i+1)%2  == t%2) {
            int b = (i+t)/2+1;
            double res = f[b];
            for (int j = b+1; j <= i+1; ++j) res += f[j];
            //cerr << i+1 << " -> " << fixed << setprecision(7) << res << '\n';
            ans = max(ans, res);
        }
    }
    //for (int i = (t+n+1)/2; i <= n; ++i) ans += f[i];
    cout << fixed << setprecision(7) << ans << '\n';
    //cerr << opc << " ops\n";

    return 0;
}