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

int main() {
    int n,m;
    cin>>n>>m;
    vector<int> a(n),b(m);
    for ( int i=0; i<n; i++ ) cin>>a[i];
    for ( int j=0; j<m; j++ ) cin>>b[j];
    int l=n/__gcd(n,m)*m;
    for ( int i=0; i<l; i++ ) {
        if ( a[i%n]==b[i%m] ) {
            cout<<i+1<<'\n';
            exit(0);
        }
    }
    cout<<-1<<'\n';
    return 0;
}