#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <stack>
#include <tuple>
#include <deque>
#include <array>
#include <numeric>
#include <bitset>
#include <iomanip>
#include <cassert>
#include <chrono>
#include <random>
#include <limits>
#include <iterator>
#include <functional>
#include <sstream>
#include <fstream>
#include <complex>
#include <cstring>
#include <unordered_map>
#include <unordered_set>
using namespace std;

#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC target("avx512f,avx512dq,avx512cd,avx512bw,avx512vl")

using ll = long long;
constexpr int INF = 1001001001;
// constexpr int mod = 1000000007;
constexpr int mod = 998244353;

template<class T>
inline bool chmax(T& x, T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template<class T>
inline bool chmin(T& x, T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}

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

    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 j = 0; j < n; ++j){
        for(int i = 0; i < n; ++i){
            a.emplace_back(a[i]);
        }
    }
    n = a.size();
    for(int j = 0; j < m; ++j){
        for(int i = 0; i < m; ++i){
            b.emplace_back(b[i]);
        }
    }
    m = b.size();

    for(int i = 0; i < min(n, m); ++i){
        if(a[i] == b[i]){
            cout << i + 1 << endl;
            return 0;
        }
    }

    cout << -1 << endl;

    return 0;
}