#include <iostream>
#include <vector>
#include <cassert>
using namespace std;
using ll = long long int;

int main(){
    int n, m;
    cin >> n >> m;
    assert(1 <= n <= 5000);
    assert(1 <= m <= 5000);
    vector<int> a(n), b(m);
    for(int i = 0; i < n; i++){
        cin >> a[i];
        assert(1 <= a[i] <= 10000);
    }
    for(int i = 0; i < m; i++){
        cin >> b[i];
        assert(1 <= b[i] <= 10000);
    }
    int ans = -1;
    for(int i = 0; i < n*m; i++){
        if(a[i%n] == b[i%m]){
            ans = i+1;
            break;
        }
    }
    cout << ans << endl;

    return 0;
}