#include <bits/stdc++.h>
#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using ll = long long;
using namespace std;

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