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#include <bits/stdc++.h>

using namespace std;

int main(){
    cin.tie(0)->sync_with_stdio(0);

    int n, t;
    cin>>n>>t;

    vector<float> values(n);
    for(int i = 0; i<n; i++){
        cin>>values[i];
    }

    sort(values.rbegin(), values.rend());

    vector<float> dp(2*n+10, 0), dp2(2*n+10, 0);

    int mid = n+4;
    dp[n+4] = 1;
    vector<float>* d1 = &dp;
    vector<float>* d2 = &dp2;

    int lower_bnd = n+4 - (n+10)/2;
    int upper_bnd = n+4 + (n+10)/2;
    float out = 0;
    for(int i = 0; i<n; i++){
        float tmp = 0;

        int sp =n+4 - i*2 - ((i+1)%2);
        int ep = n+4 + i*2 + ((i+1)%2);
        for(int j = sp; j<=ep; j+=2){
            (*d2)[j] = (*d1)[j-1] * values[i] + (*d1)[j+1] * (1.-values[i]);
            if(j >= t+mid) tmp += (*d2)[j];
        }
        out = max(out, tmp);
        (*d1).clear();
        swap(d1, d2);
    }

    cout<<fixed<<setprecision(15)<<out<<endl;
    return 0;
}