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#include <bits/stdc++.h>
using namespace std;
#define ull unsigned long long
#define ll long long
#define ld long double
#define mn2 262144
#define nw '\n'
int main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n, t;
    cin>>n>>t;
    vector<ld> v(n);
    for(auto &x:v) cin>>x;
    sort(v.rbegin(), v.rend());
    ld max_prob=0.0;
    vector<ld> dp={1.0};
    for(int i=0; i<n; ++i) {
        vector<ld> dp2(dp.size()+1, 0.0);
        ld vi=v[i];
        dp2[0]=dp[0]*(1-vi);
        for (int j=1; j<(int)dp2.size()-1; ++j) dp2[j]=dp[j]*(1-vi)+dp[j-1]*vi;
        dp2.back()=dp.back()*vi;
        dp=move(dp2);
        int k=i+1;
        if(k>=t){
            int c=(t+k+1)/2;
            if(c>k) continue;
            ld prob=0.0;
            for(int j=c; j<=k; ++j) if (j<dp.size()) prob+=dp[j];
            if(prob>max_prob) max_prob=prob;
        }
    }
    cout<<fixed<<setprecision(20)<<max_prob<<endl;
    return 0;
}