#include <cassert>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <queue>
#include <set>
#include <string.h>
#include <vector>

using namespace std;
typedef long long ll;


int main() {
  int N, M;
  cin >> N >> M;
  vector<int> A(N);
  vector<int> B(M);

  for (int i = 0; i < N; ++i) {
    cin >> A[i];
  }

  for (int i = 0; i < M; ++i) {
    cin >> B[i];
  }

  for (int i = 0; i < N * M; ++i) {
    if (A[i % N] != B[i % M]) continue;

    cout << i + 1 << endl;
    return 0;
  }

  cout << -1 << endl;

  return 0;
}