Problem: The rules of Sith Tournament are well known to everyone. n Sith take part in the Tournament. The Tournament starts with the random choice of two Sith who will fight in the first battle. As one of them loses, his place is taken by the next randomly chosen Sith who didn't fight before. Does it need to be said that each battle in the Sith Tournament ends with a death of one of opponents? The Tournament ends when the only Sith remains alive.

Jedi Ivan accidentally appeared in the list of the participants in the Sith Tournament. However, his skills in the Light Side of the Force are so strong so he can influence the choice of participants either who start the Tournament or who take the loser's place after each battle. Of course, he won't miss his chance to take advantage of it. Help him to calculate the probability of his victory.

Input

The first line contains a single integer n (1 ≤ n ≤ 18) — the number of participants of the Sith Tournament.

Each of the next n lines contains n real numbers, which form a matrix pij (0 ≤ pij ≤ 1). Each its element pij is the probability that the i-th participant defeats the j-th in a duel.

The elements on the main diagonal pii are equal to zero. For all different i, j the equality pij + pji = 1 holds. All probabilities are given with no more than six decimal places.

Jedi Ivan is the number 1 in the list of the participants.

Output

Output a real number — the probability that Jedi Ivan will stay alive after the Tournament. Absolute or relative error of the answer must not exceed 10 - 6.

Examples

Input

3
0.0 0.5 0.8
0.5 0.0 0.4
0.2 0.6 0.0


Output

0.680000000000000

Solution (in JAVA):

Solution:

import java.io.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class EducationalRound13_div2_E {

    public static void main(String[] args) throws IOException {
        FastReader in = new FastReader(System.in);
        PrintWriter out = new PrintWriter(System.out);
        solve(in, out);
        out.flush();
    }


    // input
    private static int n;
    private static double[][] pDeffeats;
    // [mask][i] ~ if "mask" people fought and the "i" won the last battle,
    //             what is probability of Jedi being the overall winner
    private static Double[][] pJediWins;

    public static void solve(FastReader in, PrintWriter out) {
        n = in.readInt();
        pDeffeats = new double[n][n];
        for (int i = 0 ; i < n ; i++) {
            for (int j = 0 ; j < n ; j++) {
                pDeffeats[i][j] = Double.parseDouble(in.readString());
            }
        }

        double solution = 0;
        if (n == 1) {
            solution = 1;
        } else {
            pJediWins = new Double[1 << n][n];

            // solve
            for (int firstContestant = 0 ; firstContestant < n ; firstContestant++) {
                solution = Math.max(solution, pJediWins(1 << firstContestant, firstContestant));
            }
        }

        out.println(solution);
    }

    private static double pJediWins(int mask, int winner) {
        if (pJediWins[mask][winner] == null) {
            double prob = 0;
            if (mask == ((1 << n) - 1)) {
                // everybody already fought, so Jedi is the winner iff Jedi is the winner :)
                prob = (winner == 0) ? 1.0 : 0.0;
            } else {
                for (int next = 0 ; next < n ; next++) {
                    if (next != winner && ((1 << next) & mask) == 0) {
                        prob = Math.max(prob,
                                pJediWins(mask | (1 << next), winner) * pDeffeats[winner][next] +
                                pJediWins(mask | (1 << next), next)   * pDeffeats[next][winner]);
                    }
                }
            }
            pJediWins[mask][winner] = prob;
        }
        return pJediWins[mask][winner];
    }

    /**
     * Custom buffered reader. Faster than Scanner and BufferedReader + StringTokenizer.
     */
    static class FastReader {
        private final InputStream stream;
        private int current;
        private int size;
        private byte[] buffer = new byte[1024 * 8];

        public FastReader(InputStream stream) {
            this.stream = stream;
            current = 0;
            size = 0;
        }

        public int readInt() {
            int sign = 1;
            int abs = 0;
            int c = readNonEmpty();
            if (c == '-') {
                sign = -1;
                c = readAny();
            }
            do {
                if (c < '0' || c > '9') {
                    throw new IllegalStateException();
                }
                abs = 10 * abs + (c - '0');
                c = readAny();
            } while (!isEmpty(c));
            return sign * abs;
        }

        public int[] readIntArray(int n) {
            int[] array = new int[n];
            for (int i = 0 ; i < n ; i++) {
                array[i] = readInt();
            }
            return array;
        }

        public char readChar() {
            return (char) readNonEmpty();
        }

        public String readString() {
            StringBuffer sb = new StringBuffer();
            int c;
            do {
                c = readAny();
            } while (isEmpty(c));
            do {
                sb.append((char) c);
                c = readAny();
            } while (!isEmpty(c));
            return sb.toString();
        }

        private int readAny() {
            try {
                if (current >= size) {
                    current = 0;
                    size = stream.read(buffer);
                    if (size < 0) {
                        return -1;
                    }
                }
            } catch (IOException e) {
                throw new RuntimeException("Failed to readAny next byte", e);
            }
            return buffer[current++];
        }

        private int readNonEmpty() {
            int result;
            do {
                result = readAny();
            } while (isEmpty(result));
            return result;
        }

        private static boolean isEmpty(int c) {
            return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == -1;
        }
    }
}