#include<iostream>
#include<vector>
#include<algorithm>

using namespace std;
using ll = long long;


int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

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