#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;

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