/* FILE: randSeq.cpp   last change: 23-July-2012   author: Romeo Rizzi
 * This program generates a sequence of n random integers.
 * Usage syntax:
 *   > randSeq out_file n k MIN_MAV MAX_VAL seed
 */

#include <fstream>
#include <cassert>
#include <iostream>
#include <cmath>
#include <stdlib.h>

using namespace std;

const int MAX_N = 1000;
const int MAX_L = 1000;

int N, L;

char source[MAX_N][MAX_L];
char target[MAX_N][MAX_L];

void trigger(char m[][MAX_L], int p);
void printM(char m[][MAX_L]);
bool testWithTarget(char m1[][MAX_L]);
void sortM(char m[][MAX_L]);

int main(int argc, char** argv) {
  
    ifstream fin("input.txt"); assert(fin);

    fin >> N >> L;

    for(int i = 0; i < N; i++)
        fin >> source[i];

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

    fin.close();

    //cout << "target disordinato:\n";
    //printM(target);
    
    sortM(target);

    //cout << "target ordinato\n";
    //printM(target);

    int max_cmb = pow(2, L);
    //cout << "origin:\n";
    //printM(source);
    //cout << "--\n--\n";

    int minMosse = L;
    int nowMosse = 0;

    bool almenoUnaSoluzione = false;

    for(int cmb = 0; cmb < max_cmb; cmb++) {

        nowMosse = 0;

        // (cmb >> j) & 0x1 => read j-esimo bit
        //cout << "cmb: " << cmb << "\n";
        for(int j = 0; j < L; j++) {

            int p = (cmb >> j) & 0x01;

            if(p == 0)
                continue;

            trigger(source, j);
            nowMosse++;
            //printM(source);
            //cout << "--\n";

        }

        if(testWithTarget(source)) {
            //cout << "i se somea\n";
            almenoUnaSoluzione = true;
            if(nowMosse < minMosse)
                minMosse = nowMosse;
        }
        // torno indietro
        for(int j = 0; j < L; j++) {

            int p = (cmb >> j) & 0x01;

            if(p == 0)
                continue;

            trigger(source, j);
        }
    }

    ofstream fout("output.txt"); assert(fout);

    if(!almenoUnaSoluzione) {
        //cout << "NOT POSSIBLE\n";
        fout << "NOT POSSIBLE";
    }
    else {
        //cout << minMosse << "\n";
        fout << minMosse;
    }

    fout.close();

}

void trigger(char m[][MAX_L], int p) {

    for(int n = 0; n < N; n++) {

        if(m[n][p] == '1')
            m[n][p] = '0';
        else
            m[n][p] = '1';

    }

}

void printM(char m[][MAX_L]) {

    for(int i = 0; i < N; i++) {
        for(int j = 0; j < L; j++)
            cout << m[i][j];

        cout << "\n";
    }

}

bool testWithTarget(char m[][MAX_L]) {

    //cout << "disordinato\n";
    //printM(m);

	sortM(m);

    //cout << "ordinato\n";
    //printM(m);

    for(int i = 0; i < N; i++)
        for(int j = 0; j < L; j++)
            if(m[i][j] != target[i][j])
                return false;

    return true;

}

int compareMyType (const void * a, const void * b)
{
    char *r1 = (char*)a;
    char *r2 = (char*)b;

    int same = 0;

    for(int i = 0; i < L; i++) {

        if(r1[i] > r2[i]) {
            return 1;
        }
        if(r1[i] < r2[i]) {
            return -1;
        }
        if(r1[i] == r2[i])
            same++;    

    }

    if(same == L)
        return 0;

    return -1;
}

void sortM(char m[][MAX_L]) {

    qsort(m, N, MAX_L, compareMyType);

}