#include <bits/stdc++.h>
#define rep(i, l, r) for (int i = (l); i < (r); i++)
using namespace std;

typedef long long ll;

int main() {
    int N, M;
    cin >> N >> M;
    vector<int> A(N), B(M);
    rep(i, 0, N) cin >> A[i];
    rep(i, 0, M) cin >> B[i];
    rep(i, 0, N * M) {
        if (A[i % N] == B[i % M]) {
            cout << i + 1 << endl;
            return 0;
        }
    }
    cout << -1 << endl;
}