#include <iostream>
#include <vector>

using namespace std;

void solve() {
    int n, m;
    cin >> n >> m;

    vector<int> xs(n), ys(m);
    for (auto& x : xs) cin >> x;
    for (auto& y : ys) cin >> y;

    for (int i = 0; i < n * m; ++i) {
        if (xs[i % n] == ys[i % m]) {
            cout << i + 1 << "\n";
            return;
        }
    }

    cout << "-1\n";
}

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

    solve();

    return 0;
}