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

long double P[50009], T[50009];

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    int n, t, a = 1, b, c, d, dmax;
    long double wyn = 0.0, x;
    cin>>n>>t;
    dmax = t + (n + 1 - t) / 2;
    for(int i=1; i<=n; i++) {
        cin>>P[i];
        if(abs(0.0 - P[i]) < 0.0000000001) {
            i--;
            n--;
        }
    }
    sort(P+1, P+n+1);
    T[0] = 1.0;
    for(int i=n; i>=1; i--) {
        b = t + (a + 1 - t) / 2;
        if(a > n - b) c = a - n + b;
        else c = 1;
        d = min(a, dmax);
        x = 1.0 - P[i];
        for(int j=d; j>=c; j--) T[j] = P[i] * T[j-1] + x * T[j];
        if(b >= 0 && b <= n && wyn < T[b]) wyn = T[b];
        else if(a >= t && (a - t) % 2 == 0) break;
        a++;
        if(abs(1.0 - wyn) < 0.00000001) break;
    }
    cout<<fixed;
    cout<<setprecision(8)<<wyn;
    return 0;
}