#include <bits/stdc++.h>
    using namespace std;
    #include <math.h>
    #include <iomanip>
    #include <cstdint>
    #include <string>
    #include <sstream>
    template<class T> inline bool chmax(T& a, T b) { if (a <= b) { a = b; return 1; } return 0; }
    template<class T> inline bool chmin(T& a, T b) { if (a >= b) { a = b; return 1; } return 0; }
    #define rep(i,n) for (int i = 0; i < (n); ++i)
    typedef long long ll;
    using P=pair<ll,ll>;
    const int INF=1001001001;
    const int mod=998244353;

    void solve(){
        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;
            }
        }
        cout<<-1<<endl;
    }
    int main(){
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        solve();
        return 0;
    }