#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int n, m;
    cin >> n >> m;
    vector<int> a(n), b(m);
    for (auto &&i : a) scanf("%d", &i);
    for (auto &&i : b) scanf("%d", &i);
    int c1 = 0, c2 = 0;
    for (int i = 0; i < n*m; ++i) {
        if(a[c1] == b[c2]){
            cout << i+1 << "\n";
            return 0;
        }
        if((++c1) == n) c1 = 0;
        if((++c2) == m) c2 = 0;
    }
    puts("-1");
    return 0;
}