#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int n, m;
  cin >> n >> m;
  vector<int> a(n), b(m);
  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];
  int l = lcm(n, m);
  rep(i, l) {
    if (a[i % n] == b[i % m]) {
      cout << i + 1 << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}