#include <bits/stdc++.h>
using namespace std;

#define int long long
#define pb push_back
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()

void out(vector<int> a) {
    for (auto it = a.begin(); it != a.end(); ++it) cout << (*it) << " ";
    cout << "\n";
}

int n, m;
string s, t;
int sz;
const int b = 5, mod = 1354828, mod2 = mod * mod;
vector<int> power;
vector<int> hash1, hash2;

inline void read() {
    cin >> n >> m >> s >> t;
    sz = max(n, m);
    power.resize(sz + 1);
    hash1.resize(sz + 1);
    hash2.resize(sz + 1);
}

int trans(char c) {
    if (c == 'A') return 1;
    if (c == 'C') return 2;
    if (c == 'G') return 3;
    if (c == 'T') return 4;
}

void calc_power() {
    power[0] = 1;
    for (int i = 1; i <= sz; ++i)
        power[i] = (power[i-1] * b) % mod;
}

void calc_hash(vector<int> &h, string &str) {
    h[0] = trans(str[0]);
    for (int i = 1; i < str.size(); ++i) {
        int c = trans(str[i]);
        h[i] = (h[i - 1] * b + c) % mod;
    }
}

int get_hash(vector<int> &h, int l, int r) {
    if (l == 0) return h[r];
    else return ((mod2 + h[r] - (h[l-1] * power[r-l+1] % mod))+ mod) % mod;
}

bool used[mod];

bool f(int mid) {
    memset(used, false, sizeof(used));
    int cnt = 0;
    for (int i = 0; i <= n - mid; ++i) {
        int id = get_hash(hash1, i, i + mid - 1);
        if (!used[id]) ++cnt;
        used[id] = true;
    }
    for (int i = 0; i <= m - mid; ++i) {
        int id = get_hash(hash2, i, i + mid - 1);
        if (used[id]) --cnt;
        used[id] = false;
    }
    if (cnt == 0) return true;
    else return false;
}

string res(int k) {
    memset(used, false, sizeof(used));
    for (int i = 0; i <= m - k; ++i) {
        int id = get_hash(hash2, i, i + k - 1);
        used[id] = true;
    }
    for (int i = 0; i <= n - k; ++i) {
        int id = get_hash(hash1, i, i + k - 1);
        if (!used[id]) return s.substr(i, k);
    }
}

vector<string> ans;

inline void solve() {
    calc_power();
    calc_hash(hash1, s);
    calc_hash(hash2, t);

    int l = 1, r = min(n, m) + 1;
    for (int i = 0; i<20; ++i) {
        int mid  = (l + r) / 2;
        if (f(mid)) l = mid + 1;
        else r = mid;
    }
    if (r == min(n, m) + 1) {
        if (n > m) cout << s.substr(0, m+1);
        else cout << "NONE";
    }
    else cout << res(r);
}

signed main() {
ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
cout << fixed << setprecision(20);
//freopen("input.txt", "r", stdin);
//freopen("output.txt", "w", stdout);
    read();
    solve();
}