#include <iostream>
#include <iomanip>
#include <cstdio>
#include <queue>
#include <cstring>
#include <vector>
#include <map>
#include <algorithm>
#include <cctype>
#include <cmath>
#include <bitset>
#include <set>
#include <deque>
#include <stack>
#include <atcoder/all>
#include <array>
using namespace std;
#define rep(i,n) for(int i = 0; i < (int)(n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < (t); ++i)
#define dsrep(i,t,s) for(int i = (t)-1; i >= (s); --i)
#define rng(a) a.begin(),a.end()
#define rrng(a) a.rbegin(),a.rend()
#define isin(x,l,r) ((l) <= (x) && (x) < (r))
#define gridinside(x,h,y,w) ((0 <= x && x < h && 0 <= y && y < w))
int dx4[4]={1,0,-1,0};
int dy4[4]={0,-1,0,1};
using ll = long long;
using uint = unsigned;
using ull = unsigned long long;
using P = pair<int,int>;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
const ll mod = 998244353;
// const ll mod = 1e9 + 7;

////////////////////////////////////////////
int n, m;
int gcd(int a, int b) {
  if(b == 0) return a;
  return gcd(b, a % b);
}

int lcm(int a, int b) {
  if(a < b) swap(a, b);
  return a * b / gcd(a, b);
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> n >> m;
  vector<int> a(n);
  vector<int> b(m);

  rep(i, n) cin >> a[i];
  rep(i, m) cin >> b[i];

  int lc = lcm(n, m);
  rep(i, lc) {
    if(a[i % n] == b[i % m]) {
      cout << i + 1 << endl;
      return 0;
    }
  }

  cout << -1 << endl;
}