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#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for (int i = (a); i <= (b); ++i)
#define REPD(i,a,b) for (int i = (a); i >= (b); --i)
#define FORI(i,n) REP(i,1,n)
#define FOR(i,n) REP(i,0,int(n)-1)
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define SZ(x) int((x).size())
#define DBG(v) cerr << #v << " = " << (v) << endl;
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define fi first
#define se second

const int N = 50500;

double p[N], d[2][N*2];
int n,nn,t;

int main() {
	scanf("%d%d", &n, &t);
	nn = n+1;
	FORI(i,n) scanf("%lf", &p[i]);
	sort(p+1,p+n+1);
	reverse(p+1,p+n+1);
	double res = 0;
	d[0][nn] = 1;
	FORI(k,n) {
		REP(i,-k,k) d[1][nn+i] = d[0][nn+i];
		//printf("%d : ", k);
		double cur = 0;
		REP(i,-k,k) {
			d[0][nn+i] = p[k] * d[1][nn+i-1] + (1-p[k]) * d[1][nn+i+1];
			if (i>=t) cur += d[0][nn+i];
			//printf("%.4lf ", d[0][nn+i]);
		}
		res = max(res, cur);
		if (res+1e-7>1) break;
		//printf("\n");
	}
	printf("%.7lf\n", res);
	return 0;
}