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#include<iostream>
#include<iomanip>
#include<vector>
#include<algorithm>

#define REP(i,n) for(int i=0;i<(n);++i)
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)

using namespace std;

const int MAX_N = 50000;

typedef double royale;

vector<royale> P;

royale T[1+MAX_N], U[1+MAX_N];

royale best, q, z;

int t, n, m;

int main(void) {	
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	
	cin >> n >> t;
	P.resize(n);
	REP(i, n) cin >> P[i];	
	sort(P.begin(), P.end());	

	REP(i,n) T[i] = 0.0;
	T[0] = 1.0;
	
	best = 0.0;
	
	FOR(m, 1, n) {
		q = P[n-m];
		U[0] = T[0]*(1-q);
		FOR(k, 1, m) {
			U[k] = T[k]*(1-q) + T[k-1]*q;
		}
		REP(i,n) T[i] = U[i];
		z = 0.0;
		REP(i,n) if (i >= ((t + m + 1) / 2)) z += T[i];
		if (z > best) best = z;		
	}

	cout << fixed << setprecision(7) << best << endl;
		
	return 0;
}