#include <bits/stdc++.h>

using namespace std;

int N,M;
char spot[500][500], plain[500][500];
long long expo[500];
bool v[500][500];
const long long MOD = 1000000007;
long long h_sp[500][500][500], h_pl[500][500][500];
int convert(char a)
{
    if(a=='A') return 0;
    if(a=='T') return 1;
    if(a=='G') return 2;
    return 3;
}
void gen(int a,int b)
{
    if(v[a][b] || b==M)
        return;

    v[a][b] = 1;

    for (int i=0;i<N;i++)
    {
        if (a < b)
        {
            h_sp[i][a+1][b] = (h_sp[i][a][b] - expo[b-a]*convert(spot[i][a]) + MOD) % MOD;
            h_pl[i][a+1][b] = (h_pl[i][a][b] - expo[b-a]*convert(plain[i][a]) + MOD) % MOD;
        }
        if (b < N)
        {
            h_sp[i][a][b+1] = (h_sp[i][a][b]*4 + convert(spot[i][b+1]) + MOD) % MOD;
            h_pl[i][a][b+1] = (h_pl[i][a][b]*4 + convert(plain[i][b+1]) + MOD) % MOD;
        }
    }
    if (a < b)
        gen(a+1,b);
    if (b < N)
        gen(a,b+1);
}
int main()
{
//    ofstream fout(cownomics.out");
//    ifstream fin("cownomics.in");

    cin >> N >> M;

    string x;
    for (int i=0;i<N;i++)
    {
        cin >> x;
        for (int j=0;j<M;j++)
            spot[i][j] = x[i];
    }
    for (int i=0;i<N;i++)
    {
        cin >> x;
        for (int j=0;j<M;j++)
            plain[i][j] = x[i];
    }

    int b = 1;
    for (int i=0;i<M;i++)
    {
        expo[i] = b;
        b = (b*4) % MOD;
    }

    for (int i=0;i<N;i++)
    {
        h_sp[i][0][0] = convert(spot[i][0]);
        h_pl[i][0][0] = convert(plain[i][0]);
    }
    gen(0,0);

    unordered_set<long long> hs;
    int res = M;
    for (int a=0;a<M;a++)
        for (int b=a;b<M;b++)
        {
            bool can_explain = 1;
            hs.clear();
            for (int i = 0; i < N; i++)
                hs.insert(h_sp[i][a][b]);
            for (int i = 0; i < N; i++)
                if (hs.find(h_pl[i][a][b]) != hs.end()) {
                    can_explain = 0;
                    break;
                }
            if (can_explain)
                res = min(res,b-a+1);
        }

    cout << res << "\n";
    return 0;
}