#include <bits/stdc++.h>

#include <atcoder/math>

#define REP_(i, a_, b_, a, b, ...) \
  for (int i = (a), END_##i = (b); i < END_##i; ++i)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
#define ALL(x) std::begin(x), std::end(x)
using i64 = long long;

template <typename T, typename U>
inline bool chmax(T &a, U b) {
  return a < b and ((a = std::move(b)), true);
}
template <typename T, typename U>
inline bool chmin(T &a, U b) {
  return a > b and ((a = std::move(b)), true);
}
template <typename T>
inline int ssize(const T &a) {
  return (int)std::size(a);
}

template <typename T>
std::istream &operator>>(std::istream &is, std::vector<T> &a) {
  for (auto &x : a) is >> x;
  return is;
}
template <typename T, typename U>
std::ostream &operator<<(std::ostream &os, const std::pair<T, U> &a) {
  return os << "(" << a.first << ", " << a.second << ")";
}
template <typename Container>
std::ostream &print_seq(const Container &a, std::string_view sep = " ",
                        std::string_view ends = "\n",
                        std::ostream &os = std::cout) {
  auto b = std::begin(a), e = std::end(a);
  for (auto it = std::begin(a); it != e; ++it) {
    if (it != b) os << sep;
    os << *it;
  }
  return os << ends;
}
template <typename T, typename = void>
struct is_iterable : std::false_type {};
template <typename T>
struct is_iterable<T, std::void_t<decltype(std::begin(std::declval<T>())),
                                  decltype(std::end(std::declval<T>()))>>
    : std::true_type {};

template <typename T, typename = std::enable_if_t<
                          is_iterable<T>::value &&
                          !std::is_same<T, std::string_view>::value &&
                          !std::is_same<T, std::string>::value>>
std::ostream &operator<<(std::ostream &os, const T &a) {
  return print_seq(a, ", ", "", (os << "{")) << "}";
}

#ifdef ENABLE_DEBUG
#include "debug_dump.hpp"
#else
#define DUMP(...)
#endif

using namespace std;

template <int sign = 1>
struct Infinity {
  template <typename T>
  constexpr operator T() const {
    static_assert(sign == 1 or not std::is_unsigned_v<T>,
                  "must be positive in an unsigned type");
    if constexpr (std::numeric_limits<T>::has_infinity) {
      return T(sign) * std::numeric_limits<T>::infinity();
    } else {
      return T(sign) * (std::numeric_limits<T>::max() / T(2));
    }
  }
  constexpr Infinity<sign * -1> operator-() const { return {}; }
  template <typename T>
  friend bool operator==(const T &x, const Infinity &y) {
    return x == T(y);
  }
  template <typename T>
  friend bool operator!=(const T &x, const Infinity &y) {
    return x != T(y);
  }
};
const Infinity<> INF;

i64 solve() {
  int n, m;
  cin >> n >> m;
  vector<int> A(n), B(m);
  cin >> A >> B;
  i64 ans = INF;
  REP(i, n) REP(j, m) {
    if (A[i] != B[j]) continue;
    vector<i64> xr = {i, j};
    vector<i64> xm = {n, m};
    auto [y, z] = atcoder::crt(xr, xm);
    if (y == 0 and z == 0) continue;
    chmin(ans, y);
  }
  if (ans == INF) {
    return -1;
  }
  return ans + 1;
}

int main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr);
  cout << solve() << "\n";
}