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

int main()
{
	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];
	}

	int INF = INT32_MAX / 2;
	int ans = INF;
	for( int i = 0; i < N * M; i++ ) {
		if( A[i % N] == B[i % M] ) {
			ans = min( ans, i + 1 );
		}
	}
	if( ans == INF ) ans = -1;

	cout << ans << endl;
}