#include <bits/stdc++.h>
using namespace std;
using ll = long long int;
using iPair = pair<int,int>;
using lPair = pair<ll, ll>;
using ivector = vector<int>;
using lvector = vector<ll>;
using istack = stack<int>;
using iqueue = queue<int>;
using ivv = vector<vector<int>>;
using lvv = vector<vector<ll>>;
const int INF = 0x3f3f3f3f;
const ll LINF = 0x3f3f3f3f3f3f3f3f;
vector<iPair> dir = {{1,0}, {-1,0}, {0,1}, {0,-1}};
#define dump(x) cout << #x << " = " << (x) << endl
#define ALL(x) begin(x),end(x)
#define rep(i,s,e) for(ll i=(s), i_stop=(e); i<i_stop; ++i)
#define repRev(i,s,e) for(ll i=(e)-1, i_stop=(s); i>=i_stop; --i)
#define range(i,s,n) for(ll i=(s), i_stop=(s)+(n); i<i_stop; ++i)
#define rangeRev(i,s,n) for(ll i=(s), i_stop=(s)-(n); i>i_stop; --i)
#define foreach(x,container) for(auto &&x:container)
template<typename T> bool chmax(T& a, const T b) {if(a<b) {a=b;return true;} return false;}
template<typename T> bool chmin(T& a, const T b) {if(a>b) {a=b;return true;} return false;}
template<typename T> void printArr(vector<T> &arr){
    for(auto &x:arr) {cout << x << " ";} cout << endl;
}

/*
因爲涉及到餘數，寫代碼從0開始。
*/

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a%b);
}


void solve() {
    ll n,m; cin>>n>>m;

    
    ivector a(n); range(i, 0, n) cin>>a[i];
    ivector b(m); range(i, 0, m) cin>>b[i];
    ll lcm = n * m / gcd(n,m);

    ll ans = -1;
    for(ll i = 0; i < lcm; ++i) {
        ll x = i%n; ll y = i%m;
        if(a[x] == b[y]) {
            ans = i+1; break;
        }
    }

    cout << ans << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    solve();
    return 0;
}