#include <cassert>
#ifndef NDEBUG
#  include <iostream>  // uso di cin e cout non consentito in versione finale
#endif
#include <fstream>
#include <climits>
#include <vector>

using namespace std;
 
int main()
{
	int n, l;
	int result = INT_MAX;
	int count = 0;

	ifstream fin("input.txt");
	ofstream fout("output.txt");

	fin>>n>>l;
	vector<string> original(n), target(n);

	for(int i=0; i<n; i++) fin>>original[i];
	for(int i=0; i<n; i++) fin>>target[i];

	for(int i=0; i<n; i++)
	{             
		vector<bool> flip(l);

		for(int j=0; j<l; j++) flip[j] = (original[0][j]!=target[i][j]);

		for(int j=0; j<n; j++)
		{
			string verifier = original[j];
			for(int k=0; k<l; k++) verifier[k] = (char)(verifier[k]^flip[k]);
			if(verifier!=target[j]) goto next_target;
		}

		count = 0;
		for(int j=0; j<l; j++) count += flip[j];
		result = min(result, count);

		next_target:
		continue;
	}

	if(result==INT_MAX) fout<<"NOT POSSIBLE\n";
	else fout<<result<<"\n";

	fin.close();
	fout.close();
}