#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

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


}