import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.Closeable;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;

public class Main {
	static ContestScanner in;
	static Writer out;
	public static void main(String[] args) {
		Main main = new Main();
		try {
			in = new ContestScanner();
			out = new Writer();
			main.solve();
			out.close();
			in.close();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	void solve() throws IOException {
		m = in.nextInt();
		n = in.nextInt();
		win = new double[m][n];
		for(int i = 0; i < m; i++) {
			for(int j = 0; j < n; j++) {
				win[i][j] = in.nextDouble();
			}
		}
		dp = new double[n + 1][1 << m];
		for(int i = 0; i <= n; i++) {
			Arrays.fill(dp[i], -1);
		}
		Arrays.fill(dp[n], 1);
		System.out.printf("%.20f\n", dfs(0, 0));
	}
	
	int n, m;
	double[][] dp;
	double[][] win;
	double dfs(int enm, int state) {
		if(dp[enm][state] >= 0) return dp[enm][state];
		double ans = 0;
		for(int i = 0; i < m; i++) {
			if((state & 1 << i) > 0) continue;
			double prob = 1;
			double exp = 0;
			for(int j = enm; j < n; j++) {
				double w = prob * win[i][j];
				double l = prob * (1 - win[i][j]);
				exp += l * dfs(j, state | 1 << i);
				prob = w;
			}
			exp += prob;
			ans = Math.max(ans, exp);
		}
		return dp[enm][state] = ans;
	}
}

@SuppressWarnings("serial")
class MultiSet<T> extends HashMap<T, Integer>{
	@Override public Integer get(Object key){return containsKey(key)?super.get(key):0;}
	public void add(T key,int v){put(key,get(key)+v);}
	public void add(T key){put(key,get(key)+1);}
	public void sub(T key){final int v=get(key);if(v==1)remove(key);else put(key,v-1);}
	public MultiSet<T> merge(MultiSet<T> set)
	{MultiSet<T>s,l;if(this.size()<set.size()){s=this;l=set;}else{s=set;l=this;}
	for(Entry<T,Integer>e:s.entrySet())l.add(e.getKey(),e.getValue());return l;}
}

class Writer extends PrintWriter{
	public Writer(String filename)throws IOException
	{super(new BufferedWriter(new FileWriter(filename)));}
	public Writer()throws IOException{super(System.out);}
}
class ContestScanner implements Closeable{
	private BufferedReader in;private int c=-2;
	public ContestScanner()throws IOException 
	{in=new BufferedReader(new InputStreamReader(System.in));}
	public ContestScanner(String filename)throws IOException
	{in=new BufferedReader(new InputStreamReader(new FileInputStream(filename)));}
	public String nextToken()throws IOException {
		StringBuilder sb=new StringBuilder();
		while((c=in.read())!=-1&&Character.isWhitespace(c));
		while(c!=-1&&!Character.isWhitespace(c)){sb.append((char)c);c=in.read();}
		return sb.toString();
	}
	public String readLine()throws IOException{
		StringBuilder sb=new StringBuilder();if(c==-2)c=in.read();
		while(c!=-1&&c!='\n'&&c!='\r'){sb.append((char)c);c=in.read();}
		return sb.toString();
	}
	public long nextLong()throws IOException,NumberFormatException
	{return Long.parseLong(nextToken());}
	public int nextInt()throws NumberFormatException,IOException
	{return(int)nextLong();}
	public double nextDouble()throws NumberFormatException,IOException 
	{return Double.parseDouble(nextToken());}
	public void close() throws IOException {in.close();}
}

Measured memory_bytes: 35000