#include <bits/stdc++.h>
using namespace std;

int n, m, w = 1e9;
int a[5000], b[5000];

int main()
{
	cin >> n >> m;

	for (int i = 0; i < n; i++)
		cin >> a[i];

	for (int i = 0; i < m; i++)
		cin >> b[i];

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < m; j++) {
			int u = (i + n * j) % m;

			if (a[i] == b[u]) {
				w = min(w, i + n * j + 1);
				break;
			}
		}
	}

	if (w == 1e9)
		cout << -1 << endl;
	else
		cout << w << endl;
}