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

#ifdef DEBUG
auto &operator<<(auto &o, pair<auto, auto> p) {
    return o << "(" << p.first << ", " << p.second <<")";
}
auto operator<<(auto &o, auto x)-> decltype(x.end(), o) {
    o << "{";int i = 0;
    for(auto e : x) o << ", "+!i++<<e;
    return o <<"}";
}
#define debug(x...) cerr << "["#x"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(x)
#else
#define debug(...) {}
#endif

#define int long long
#define all(x) x.begin(), x.end()
#define sz(x) (int)(x).size()
#define pb push_back
#define fi first
#define se second
typedef pair <int, int> pii;
typedef long double ld;

ld read_d() {
    string s; cin>>s;

    if (s[0] == '1') return 1;
    ld res = 0;
    for (int i=sz(s)-1; i>1; --i) {
        int cyf = s[i] - '0';

        res += cyf;
        res /= 10.0;
    }
    return res;
}


void test() {
    cout<<fixed<<setprecision(8);
    cerr<<fixed<<setprecision(8);
    debug("TC______________________");
    int n; cin>>n;
    int t; cin>>t;
    debug(n, t);
    vector <ld> V(n);
    
    for (int i=0; i<n; ++i) {
        V[i] = read_d();
    }

    sort(all(V));
    reverse(all(V));

    vector <vector <ld> > p(2, vector<ld>(2*n+3));
    p[0][n+1] = 1.0;
    ld best = 0.0;

    for (int i=1; i<=n; ++i) {
        int ii = i%2;
        ld pp = V[i-1], qq = (1.0 - pp);

        for (int j=1; j<=2*n+1; ++j) {
            p[ii][j] = pp * p[ii ^ 1][j-1];
        }

        for (int j=0; j<=2*n; ++j) {
            p[ii][j] += qq * p[ii ^ 1][j+1];
        }

        ld sum = 0.0;
        for (int j=n+1+t; j<=2*n+1; ++j) {
            sum += p[ii][j];
        }

        best = max(sum, best);
    }

    cout<<best<<'\n';
}

signed main() {
  ios_base::sync_with_stdio(0); cin.tie(0);
  int t = 1; 
  while (t--) {
    test();
  }
}