#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <algorithm>
#include <cassert>
using namespace std;

int main()
{
  ifstream fin("input.txt");
	ofstream fout("output.txt");
	
  int N = 0, L = 0, target = 0, n = 0, check = 0;
  string x;
  vector<string> in1, in2, tOut;

  assert(fin);

	fin >> N;
  fin >> L;

	target = L + 1;

	for (int j = 0; j < N; ++j) 
  {
		fin >> x;
		in1.push_back(x);
	}
		for (int j = 0; j < N; ++j) 
  {
		fin >> x;
		in2.push_back(x);
	}

  fin.close();

	sort(in2.begin(), in2.end());

	for (int j = 0; j < N; ++j) 
  {
	  for (int k = 0; k < N; ++k)
				tOut.push_back(in1[k]);
		for (int k = 0; k < L; ++k) 
    {
		  if (in2[0][k] != tOut[j][k]) 
      {
			  n++;
				for (int m = 0; m < N; ++m) 
        {
           if(tOut[m][k] == '1')
            tOut[m][k] = '0';
           else
            tOut[m][k] = '1';
        } 
  		}
  	}
		sort(tOut.begin(), tOut.end());
		check = 0;
		for (int k = 0; k < N; ++k) 
    {
			if (in2[k] != tOut[k])
					check++;
		}
		if (check < 1) 
      if(target<=n)
        target = target;
      else
        target = n;
		}

		if (target <= L)
			fout << target << endl;
		else 
			fout << "NOT POSSIBLE" << endl;
  fout.close();
	return 0;
}