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#include <vector>
#include <cstdio>
#include <stack>
#include <algorithm>
#include <queue>
#include <map>
#include <cmath>
#include <unordered_set>
#include <unordered_map>
#include <set>
#include <cstring>
#include <bitset>
#include <iostream>
#include <queue>
#include <iomanip>
#include <complex>

using namespace std;

#define ALL(x) x.begin(), x.end()
#define UNIQUE(c) (c).resize(unique(ALL(c)) - (c).begin())
#define FOR(i, a, b) for(int i =(a); i <=(b); ++i)
#define RE(i, n) FOR(i, 1, n)
#define RED(i, n) FORD(i, n, 1)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define REP(i, n) for(int i = 0;i <(n); ++i)
#define REPD(i, n) FORD(i, n-1,0)

#define printA(a, L, R) FOR(i,L,R) cout << a[i] << (i==R?'\n':' ')
#define printV(a) printA(a,0,a.size()-1)
#define PRESENT(c, x) ((c).find(x) != (c).end())
#define CPRESENT(c, x) (find(ALL(c),x) != (c).end())
#define bit(x, i) (x&(1<<i))
#define lowbit(x) ((x)&((x)^((x)-1)))

const int fx[4][2] = {{0,  1},
                      {0,  -1},
                      {1,  0},
                      {-1, 0}};
const int fxx[8][2] = {{0,  1},
                       {0,  -1},
                       {1,  0},
                       {-1, 0},
                       {1,  1},
                       {1,  -1},
                       {-1, 1},
                       {-1, -1}};
const int sk[8][2] = {{2,  1},
                      {2,  -1},
                      {-2, -1},
                      {-2, 1},
                      {1,  2},
                      {-1, 2},
                      {1,  -2},
                      {-1, -2}};

const int maxn = 50012;
long long mod = 998244353ll;
const long long inf = 10000000000012ll;

int n, t, mi, ma, po;
double p[maxn],res,b[2][maxn * 2], je = 1, eps = 0.000001;
bool akt;
void solve() {
    cin>>n>>t;
    REP(i, n) cin>>p[i];
    sort(p, p + n, [](auto a, auto b) {
        return a > b;
    });
    if (t%2 == 1) {
        po = 1;
        b[akt][n + 1] = p[0];
        b[akt][n - 1] = 1 - p[0];
        mi = n - 1; ma = n + 1;
        if (t == 1)res = p[0];
    } else {
        b[akt][n] = 1;
        mi = n; ma = n;
    }

    for (int i = po; i < n; i += 2) {
        FOR(j, mi, ma) {
            b[!akt][j - 2] += b[akt][j] * (je - p[i]) * (je - p[i + 1]);
            b[!akt][j] += b[akt][j] * ((je - p[i]) * p[i + 1] + (je - p[i + 1]) * p[i]);
            b[!akt][j + 2] = b[akt][j] * p[i] * p[i + 1];
        }
        double wyn = 0;
        mi-=2; ma+=2;
        FOR(j, n + t, ma) {
            wyn += b[!akt][j];
        }
        res = max(res, wyn);
        if (wyn  > eps && res - wyn > eps)break;
        akt = !akt;
    }
    cout << fixed << setprecision(20) <<res<<"\n";
}

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

    int tt = 1;
//    cin >> tt;`
    while (tt--) {
        solve();
    }
    return 0;
}