using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;

class Program
{
    #region library
    static int n = 0;
    static int r = 0;
    static int c = 0;
    static string s = "";
    static long sum = 0;
    static long cnt = 0;
    static long max = long.MinValue;
    static long min = long.MaxValue;
    static long inf = long.MaxValue / 2;
    static bool flg = false;
    static long[] arr;
    static char[,] map;
    static long[,] imap;
    static string alpha = "abcdefghijklmnopqrstuvwxyz";
    static int mod = 1000000007;

    public class Input { static readonly char[] separator = { ' ', '\r', '\n' }; readonly StreamReader sr; readonly Queue<string> queue; public Input(string path = "") { queue = new Queue<string>(); if (string.IsNullOrEmpty(path)) { sr = new StreamReader(Console.OpenStandardInput()); } else { sr = new StreamReader(path); } } public void SetText(IEnumerable<string> items) { foreach (var item in items) { SetText(item); } } public bool SetText(string s) { if (s == null) return false; foreach (var elem in s.Trim().Split(separator, StringSplitOptions.RemoveEmptyEntries)) { queue.Enqueue(elem); } return true; } public bool Any() { return queue.Any() || Read(); } bool Read() { if (!SetText(sr.ReadLine())) return false; if (!queue.Any()) return Read(); return queue.Any(); } public string Next() { if (!queue.Any() && !Read()) { return ""; } return queue.Dequeue(); } bool Accumulate(int n) { while (queue.Count() < n) { if (!Read()) return false; } return true; } public int NextInt() { return int.Parse(Next()); } public long NextLong() { return long.Parse(Next()); } public double NextDouble() { return double.Parse(Next()); } T[] NextT<T>(int n, T offset, Func<string, T> parse, Func<T, T, T> add) { if (!Accumulate(n)) return null; var a = new T[n]; for (int i = 0; i < n; i++) a[i] = add(parse(queue.Dequeue()), offset); return a; } public string[] Next(int n) { return NextT(n, "", x => x, (x, y) => x); } public int[] NextInt(int n, int offset = 0) { return NextT(n, offset, int.Parse, (x, y) => x + y); } public long[] NextLong(int n, long offset = 0) { return NextT(n, offset, long.Parse, (x, y) => x + y); } public double[] NextDouble(int n, double offset = 0.0) { return NextT(n, offset, double.Parse, (x, y) => x + y); } }
    static Input input;
    static int Int() { return input.NextInt(); }
    static long Long() { return input.NextLong(); }
    static double Double() { return input.NextDouble(); }
    static string Text() { return input.Next(); }
    static void wl(object obj = null) { Console.WriteLine(obj); }
    static void w(object obj) { Console.Write(obj); }
    static void YES() { wl("YES"); }
    static void NO() { wl("NO"); }
    static void YN(bool b) { if (b) YES(); else NO(); }
    static void Yes() { wl("Yes"); }
    static void No() { wl("No"); }
    static void yn(bool b) { if (b) Yes(); else No(); }
    static void Sum() { wl(sum); }
    static void Cnt() { wl(cnt); }
    static void Max() { wl(max); }
    static void Min() { wl(min); }
    static void swap<T>(ref T a, ref T b) { var w = a; a = b; b = w; }
    static void SetArray(long[] array = null) { if (array != null) { for (int i = 0; i < array.Length; i++) { array[i] = Long(); } } else { if (n == 0) { n = Int(); } arr = new long[n]; for (int i = 0; i < n; i++) { arr[i] = Long(); } } }
    static void ShowArray(long[] array = null) { if (array != null) { wl(string.Join(" ", array)); } else if (arr != null) { wl(string.Join(" ", arr)); } }
    static void CompressArray() { var list = arr.ToList(); list = list.OrderBy(x => x).ToList(); var dic = new Dictionary<long, long>(); var cnt = 0; for (int i = 0; i < list.Count; i++) { if (!dic.ContainsKey(list[i])) { dic.Add(list[i], cnt); cnt++; } } var arr2 = new long[arr.Length]; for (int i = 0; i < arr.Length; i++) { arr2[i] = dic[arr[i]]; } arr = arr2; }
    static void SetMap(char[,] map2 = null) { if (r == 0 && c == 0) { r = Int(); c = Int(); } if (map2 != null) { for (int i = 0; i < r; i++) { s = Text(); for (int j = 0; j < c; j++) { map2[i, j] = s[j]; } } } else { map = new char[r, c]; for (int i = 0; i < r; i++) { s = Text(); for (int j = 0; j < c; j++) { map[i, j] = s[j]; } } } }
    static void RotateMap() { var map2 = new char[c, r]; for (int i = 0; i < r; i++) { for (int j = 0; j < c; j++) { map2[j, r - i - 1] = map[i, j]; } } map = map2; }
    static void SetIMap(long[,] imap2 = null) { if (r == 0 && c == 0) { r = Int(); c = Int(); } if (imap2 != null) { for (int i = 0; i < r; i++) { for (int j = 0; j < c; j++) { imap2[i, j] = Long(); } } } else { imap = new long[r, c]; for (int i = 0; i < r; i++) { for (int j = 0; j < c; j++) { imap[i, j] = Long(); } } } }
    static void ShowMap(char[,] map2 = null) { for (int i = 0; i < r; i++) { for (int j = 0; j < c; j++) { if (map2 != null) w(map2[i, j] + " "); else w(map[i, j] + " "); } wl(); } }
    static void ShowIMap(long[,] imap2 = null) { for (int i = 0; i < r; i++) { for (int j = 0; j < c; j++) { if (imap2 != null) w(imap2[i, j] + " "); else w(imap[i, j] + " "); } wl(); } }
    #endregion

    #region main
    static void Main(string[] args) { var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }; Console.SetOut(sw); input = new Input(); try { Solve(); } catch (Exception ex) { wl(ex); if (!(args.Length >= 1 && args[0] == "/debug")) throw ex; } Console.Out.Flush(); }
    public static void Solve()
    {
        n = Int();
        var m = Int();
        var a = new int[n];
        for (int i = 0; i < n; i++)
        {
            a[i] = Int();
        }
        var b = new int[m];
        for (int i = 0; i < m; i++)
        {
            b[i] = Int();
        }

        cnt = 0;
        var cnt2 = 0;
        for (int i = 0; i < Math.Min(n * n, m * m); i++)
        {
            sum++;
            if (a[cnt] == b[cnt2])
            {
                wl(sum);
                return;
            }
            cnt++;
            cnt %= n;
            cnt2++;
            cnt2 %= m;
        }
        wl(-1);
    }
        
    #endregion

}