#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
using namespace std;
#define all(a) a.begin(), a.end()
#define int long long
const int mod = 1e9 + 9;
const int b1 = 16063807ll, b2 = 964027ll, mod1 = 1e9 + 7, mod2 = 998244353;
struct Hash {
    vector<pair<int, int>> h, p;
    Hash(int n, vector<int>& a) {
        h.resize(n + 1), p.resize(n + 1);
        h[0] = {0, 0};
        p[0] = {1, 1};
        for (int i = 0; i < n; i++) {
            h[i + 1].first = (h[i].first * b1 + a[i]) % mod1;
            h[i + 1].second = (h[i].second * b2 + a[i]) % mod2;
            p[i + 1].first = (p[i].first * b1) % mod1;
            p[i + 1].second = (p[i].second * b2) % mod2;
        }
    }
    pair<int, int> get_hash(int l, int r) {
        int left = (h[r + 1].first - (h[l].first * p[r - l + 1].first) % mod1 + mod1) % mod1;
        int right = (h[r + 1].second - (h[l].second * p[r - l + 1].second) % mod2 + mod2) % mod2;
        return {left, right};
    }
};
signed main() {
#ifdef _DEBUG
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, m; cin >> n >> m;
    vector<int> a(n), b(m);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    for (int i = 0; i < m; i++) {
        cin >> b[i];
    }
    Hash a_bck(n, a), b_bck(m, b);
    reverse(all(a)); reverse(all(b));
    Hash a_fr(n, a), b_fr(m, b);
    auto hash_pair = [&](pair<int, int>& x) {
        return (x.first + (x.second * b1) % mod) % mod;
    };
    int ans = 1;
    for (int _ = 0; _ < 2; _++) {
        auto ok = [&](int tm) {
            unordered_set<int> st;
            for (int i = tm; i + tm - 1 + _ < n; i++) {
                pair<int, int> left = a_bck.get_hash(i - tm, i - 1);
                pair<int, int> right = a_fr.get_hash(n - 1 - (i + _ + tm - 1), n - 1 - (i + _));
                swap(left, right);
                left.first = (left.first - right.first + mod1) % mod1;
                left.second = (left.second - right.second + mod2) % mod2;
                st.insert(hash_pair(left));
            }
            for (int i = tm; i + tm - 1 + _ < m; i++) {
                pair<int, int> left = b_bck.get_hash(i - tm, i - 1);
                pair<int, int> right = b_fr.get_hash(m - 1 - (i + _ + tm - 1), m - 1 - (i + _));
                left.first = (left.first - right.first + mod1) % mod1;
                left.second = (left.second - right.second + mod2) % mod2;
                if (st.count(hash_pair(left))) {
                    return true;
                }
            }
            return false;
        };
        int l = 0, r = n / 2 + 10;
        while (r - l > 1) {
            int tm = (r + l) / 2;
            if (ok(tm)) {
                l = tm;
            }
            else {
                r = tm;
            }
        }
        ans = max(ans, l * 2 + _);
    }
    cout << ans;
}