#include <iostream>
#include <fstream>
#include <cassert>
#include <typeinfo>
#include <vector>
#include <stack>
#include <cmath>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <cstdio>
#include <queue>
#include <iomanip>
#include <cctype>
#include <random>
#include <complex>
#define syosu(x) fixed<<setprecision(x)
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef pair<double,double> pdd;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<vc> vvc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<vb> vvb;
typedef vector<P> vp;
typedef vector<vp> vvp;
typedef vector<pll> vpll;
typedef pair<P,int> pip;
typedef vector<pip> vip;
const int inf=1<<29;
const ll INF=1ll<<60;
const double pi=acos(-1);
const double eps=1e-7;
const ll mod=1e9+7;
const int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};

int n,m;
vvd a;

int main(){
	cin>>n>>m;
	a=vvd(n,vd(m));
	for(int i=0;i<n;i++) for(int j=0;j<m;j++) cin>>a[i][j];
	vvd dp(1<<n,vd(m));
	for(int i=0;i<1<<n;i++) for(int j=m-1;j>=0;j--){
		for(int k=0;k<n;k++) if(i&1<<k){
			double tmp=0,p=1;
			for(int l=j;l<m;l++){
				tmp+=p*(1-a[k][l])*dp[i-(1<<k)][l];
				p*=a[k][l];
			}
			dp[i][j]=max(dp[i][j],tmp+p);
		}
	}
	cout<<syosu(11)<<dp[(1<<n)-1][0]<<endl;
}