import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.DataInputStream;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Reader in = new Reader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        ICoins solver = new ICoins();
        solver.solve(1, in, out);
        out.close();
    }

    static class ICoins {
        private double[][] dp;
        private double[] prob;
        private int n;

        public void solve(int testNumber, Reader in, PrintWriter out) {
            n = in.nextInt();
            prob = new double[n];
            for (int i = 0; i < n; ++i) {
                prob[i] = in.nextDouble();
            }
            int heads = n / 2 + 1;
            dp = new double[n + 1][n + 1];
            dp[1][0] = 1 - prob[0];
            dp[1][1] = prob[0];
            for (int i = 2; i <= n; ++i) {
                for (int j = 0; j <= i; ++j) {
                    if (j == 0) dp[i][j] = (1 - prob[i - 1]) * dp[i - 1][j];
                    else {
                        dp[i][j] = prob[i - 1] * dp[i - 1][j - 1] + (1 - prob[i - 1]) * dp[i - 1][j];
                    }
                }
            }
            double ans = 0.0;
            for (int i = heads; i <= n; ++i) {
                ans += dp[n][i];
            }
            out.println(ans);
        }

    }

    static class Reader {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer;
        private int bytesRead;

        public Reader(InputStream in) {
            din = new DataInputStream(in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) {
            try {
                din = new DataInputStream(new FileInputStream(file_name));
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public int nextInt() {
            int ret = 0;
            byte c = read();
            while (c <= ' ') {
                c = read();
            }
            boolean neg = (c == '-');
            if (neg) {
                c = read();
            }
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg) {
                return -ret;
            }
            return ret;
        }

        public double nextDouble() {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ') {
                c = read();
            }
            boolean neg = (c == '-');
            if (neg) {
                c = read();
            }

            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (c == '.') {
                while ((c = read()) >= '0' && c <= '9') {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg) {
                return -ret;
            }
            return ret;
        }

        private void fillBuffer() {
            try {
                bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
                if (bytesRead == -1) {
                    buffer[0] = -1;
                }
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }

        private byte read() {
            if (bufferPointer == bytesRead) {
                fillBuffer();
            }
            return buffer[bufferPointer++];
        }

    }
}



Measured memory_bytes: 131252