//
//
//  Codeforces: ganariya
//  AtCoder: ganariya2525
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//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <complex>
#include <regex>
#include <locale>
#include <random>

using namespace std;

#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v){std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}

using LL = long long;

//~~~~~~~~~~~~~~~~~~~~~_(＾～＾ ｣ ∠)_~~~~~~~~~~~~~~~~~~~~~


int main() {

    int N;
    cin >> N;

    vector<double> p(N);
    for (int i = 0; i < N; i++) cin >> p[i];

    //dp[i][j]
    //0-index
    //[0, i)枚目までコインで
    //j枚表が出る確率
    vector<vector<double>> dp(N + 1, vector<double>(N + 1, 0));
    dp[0][0] = 1.0;

    //0-index
    //i枚目を使うとき
    for (int i = 0; i < N; i++) {

        //j枚がすでに表である時
        for (int j = 0; j < N; j++) {

            //i枚目が表
            dp[i + 1][j + 1] += dp[i][j] * p[i];

            //i枚目が裏
            dp[i + 1][j] += dp[i][j] * (1 - p[i]);

        }
    }

    double ans = 0.0;
    for (int i = N / 2 + 1; i <= N; i++) ans += dp[N][i];

    cout << fixed << setprecision(20) << ans << endl;

    return 0;
}
















































Measured memory_bytes: 70784