/* -*- coding: utf-8 -*-
 *
 * 1544.cc:  No.1544 [Cherry 2nd Tune C] Synchroscope - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 5000;
const int MAX_M = 5000;

/* typedef */

/* global variables */

int as[MAX_N], bs[MAX_M];

/* subroutines */

template <typename T>
T gcd(T m, T n) {  // m > 0, n > 0
  if (m < n) swap(m, n);
  while (n > 0) {
    T r = m % n;
    m = n;
    n = r;
  }
  return m;
}

/* main */

int main() {
  int n, m;
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++) scanf("%d", as + i);
  for (int i = 0; i < m; i++) scanf("%d", bs + i);

  int l = n * m / gcd(n, m);

  for (int i = 0; i < l; i++)
    if (as[i % n] == bs[i % m]) { printf("%d\n", i + 1); return 0; }

  puts("-1");
  return 0;
}