#define TEST
#undef TEST //実装時にはこれをコメントアウトしないようにすること

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using sc = Scanner;

class Program
{

    static void Main(string[] args)
    {

        var q = new AnswerCollecter<int>();
        while (true)
        {
            int n = sc.NextInt();
            if (n == 0) break;
            int a = sc.NextInt();
            int b = sc.NextInt();
            int c = sc.NextInt();
            int x = sc.NextInt();
            int[] y = new int[n];
            for (int i = 0; i < n; i++)
                y[i] = sc.NextInt();

            int answer = -1;
            int numberOfAdjustedY = 0;
            int key = x;
            for (int i = 0; i < 10000+1; i++)
            {
                if (key == y[numberOfAdjustedY])
                    numberOfAdjustedY++;
                if (numberOfAdjustedY == y.Length)
                {
                    answer = i;
                    break;
                }
                key = (a * key + b) % c;
            }
            q.Enqueue(answer);
        }
        q.Answer();
#if TEST
    Console.ReadLine();
#endif
    }


}

public class AnswerCollecter<T>
{
    private Queue<T> q;



    public AnswerCollecter()
    {
        q = new Queue<T>();
    }

    public void Enqueue( T item)
    {
        q.Enqueue(item);
    }

    public void Answer()
    {
        while (q.Count != 0)
            Console.WriteLine(q.Dequeue());
    }
    public int Count()
    {
        return q.Count;
    }
}
   
public static class Scanner
{
    public static string NextString()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return tmp;
    }

    public static string[] NextStrArray()
    {
        return Console.ReadLine().Split(' ');
    }

    public static long[] NextLongArray()
    {
        string[] s = NextStrArray();
        long[] a = new long[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = long.Parse(s[i]);
        }
        return a;
    }
    public static int[] NextIntArray()
    {

        string[] s = NextStrArray();
        int[] a = new int[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = int.Parse(s[i]);
        }
        return a;
    }
    public static int NextInt()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
        
            tmp += readData;
        }
        return int.Parse(tmp);
    }
    public static double NextDouble()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return double.Parse(tmp);
    }
    public static long NextLong()
    {
        string tmp = "";
        while (true)
        {
            string readData = char.ConvertFromUtf32(Console.Read());
            if (readData == " " || readData == "\n")
                break;
            tmp += readData;
        }
        return long.Parse(tmp);
    }
    public static double[] NextDoubleArray()
    {

        string[] s = NextStrArray();
        double[] a = new double[s.Length];
        for (int i = 0; i < a.Length; i++)
        {
            a[i] = double.Parse(s[i]);
        }
        return a;
    }
}

Measured memory_bytes: 6140