#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <map>
#include <set>
#include <queue>
#include <iomanip>
#include <cstring>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i,n) for (int i = 0; i < int(n);i++)

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