import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;

/**
 * Name: Coins
 * URL: https://atcoder.jp/contests/dp/tasks/dp_i
 * rating:
 */
public class Main {

    static PrintWriter pw = new PrintWriter(System.out);

    public static void solution() {
        FastReader reader = new FastReader(System.in);

        int numTests = 1; // reads integer
        for (int i = 0; i < numTests; i++) {
            int N = reader.nextInt();
            double[] prs = new double[N];
            for (int s = 0; s < N; s++) {
                prs[s] = reader.nextDouble();
            }
            pw.println(solve(prs, N));
        }
        pw.close();
    }

    public static double solve(double[] prs, int N) {
        double[][] dp = new double[N+1][N+1];
        for (int i = 0; i <= N; i++)
            Arrays.fill(dp[i], 0.0);
        dp[0][0] = 1;
        for (int i = 1; i <= N; i++)
            for (int j = 0; j <= i; j++) {
                // xet vi tri thu i - 1
                if (j > 0) {
                    dp[i][j] = dp[i-1][j]*(1 - prs[i-1]) + dp[i-1][j-1]*prs[i-1];
                } else {
                    dp[i][j] = dp[i-1][j]*(1 - prs[i-1]);
                }
            }
        double sum = 0;
        for (int i = (N+1)/2; i <= N; i++) {
            sum += dp[N][i];
        }
        return sum;
    }

    static int combination(int n, int k) {
        return factorial(n)/(factorial(k) * factorial(n-k));
    }

    static int factorial(int n) {
        int fact = 1;
        int i = 1;
        while(i <= n) {
            fact *= i;
            i++;
        }
        return fact;
    }

    public static void main(String[] args) {
        solution();
    }

    static class FastReader {
        InputStream is;
        private byte[] inbuf = new byte[1024];
        private int lenbuf = 0, ptrbuf = 0;

        public FastReader(InputStream is) {
            this.is = is;
        }

        public int readByte() {
            if (lenbuf == -1) throw new InputMismatchException();
            if (ptrbuf >= lenbuf) {
                ptrbuf = 0;
                try {
                    lenbuf = is.read(inbuf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (lenbuf <= 0)
                    return -1;
            }
            return inbuf[ptrbuf++];
        }

        public boolean isSpaceChar(int c) {
            return !(c >= 33 && c <= 126);
        }

        public int skip() {
            int b;
            while ((b = readByte()) != -1 && isSpaceChar(b)) ;
            return b;
        }

        public String next() {
            int b = skip();
            StringBuilder sb = new StringBuilder();
            while (!(isSpaceChar(b))) {
                sb.appendCodePoint(b);
                b = readByte();
            }
            return sb.toString();
        }

        public String nextLine() {
            int b = readByte();
            StringBuilder sb = new StringBuilder();
            while (b != '\n' || b != '\r') {
                sb.appendCodePoint(b);
            }
            return sb.toString();
        }

        public int nextInt() {
            int num = 0, b;
            boolean minus = false;
            while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
            if (b == '-') {
                minus = true;
                b = readByte();
            }
            while (true) {
                if (b >= '0' && b <= '9') {
                    num = (num << 3) + (num << 1) + (b - '0');
                } else {
                    return minus ? -num : num;
                }
                b = readByte();
            }
        }

        public long nextLong() {
            long num = 0;
            int b;
            boolean minus = false;
            while ((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')) ;
            if (b == '-') {
                minus = true;
                b = readByte();
            }
            while (true) {
                if (b >= '0' && b <= '9') {
                    num = (num << 3) + (num << 1) + (b - '0');
                } else {
                    return minus ? -num : num;
                }
                b = readByte();
            }
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }

        public char[] next(int n) {
            char[] buf = new char[n];
            int b = skip(), p = 0;
            while (p < n && !(isSpaceChar(b))) {
                buf[p++] = (char) b;
                b = readByte();
            }
            return n == p ? buf : Arrays.copyOf(buf, p);
        }

        public char nextChar() {
            return (char) skip();
        }
    }
}


Measured memory_bytes: 106256