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

#define FOR(i,p,q) for(int i=(p); i<=(q); ++i)
#define ROF(i,p,q) for(int i=(p); i>=(q); --i)
#define REP(i,q) for(int i=0; i<(q); ++i)
#define pb push_back
#define as assign
#define rz resize
#define Co const
#define all(X) X.begin(), X.end()
#define rall(X) X.rbegin(), X.rend()
#define sz(X) (int)(X.size())
#define ckmax(a,b) a=max(a,b)
#define ckmin(a,b) a=min(a,b)
#define V vector
typedef long long ll;
typedef long double ld;
typedef mt19937_64 mt;
#ifndef UNCLE
 typedef basic_string<bool> vb;
 typedef basic_string<int> vi;
 typedef basic_string<ll> vl;
#else
 typedef V<bool> vb;
 typedef V<int> vi;
 typedef V<ll> vl;
#endif

int N,T;
V<ld> s;
V<V<ld>> dp;

void Input(){
    cin>>N>>T;
    T+=N;
    dp.rz(2), dp[0].as(2*N+1,0), dp[1].as(2*N+1,0);
    s.rz(N);
    for(ld &vv:s) cin>>vv;
    sort(rall(s));
}
void Solve(){
    ld res=0;
    dp[0][N]=1;
    REP(i,N){
        dp[1][0]=dp[0][1]*(1-s[i]), dp[1][2*N]=dp[0][2*N-1]*s[i];
        FOR(it,1,2*N-1) dp[1][it]=dp[0][it-1]*s[i]+dp[0][it+1]*(1-s[i]);
        swap(dp[0],dp[1]);
        ld crs=0;
        FOR(it,T,2*N) crs+=dp[0][it];//moge zrobic szybciej (nie robic tego)
        ckmax(res,crs);
    }

    // cout<<setprecision(16)<<fixed<<res<<"\n";
    cout<<setprecision(7)<<fixed<<res<<"\n";
}
int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);

    Input();
    Solve();
}