#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <set>
#include <queue>
#include <cmath>
#include <algorithm>
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define all(x) (x).begin(),(x).end()
typedef long long ll;
using P = pair<int,int>;
#define INF 1001001001
#define LINF (1LL<<60)
#define F first
#define S second
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; }

int main() {
  int n, m; cin >> n >> m;
  vector<int> a(n);
  rep(i, n) cin >> a[i];
  vector<int> b(m);
  rep(i, m) cin >> b[i];
  int ans = -1;
  rep(i, n*m+1) {
    if (a[i%n] == b[i%m]) {
      ans = i+1;
      break;
    }
  }
  cout << ans << endl;
}