#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <tuple>
#include <vector>

#define mkp make_pair
#define mkt make_tuple
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define all(v) v.begin(), v.end()
using namespace std;
typedef long long ll;
const ll MOD = 1e9 + 7;
// const ll MOD = 998244353;
template <class T> void chmin(T &a, const T &b) {
    if (a > b) a = b;
}
template <class T> void chmax(T &a, const T &b) {
    if (a < b) a = b;
}

const int L = 25e6;

void solve() {
    int N, M;
    cin >> N >> M;
    vector<int> A(N), B(M);
    rep(i, N) cin >> A[i];
    rep(i, M) cin >> B[i];

    for (int i = 0; i < L; i++) {
        if (A[i % N] == B[i % M]) {
            cout << i + 1 << endl;
            return;
        }
    }

    cout << -1 << endl;
}

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    solve();

    return 0;
}