import java.io.*;
import java.util.*;

class A
{
	private static final int MAX_COUNT = 10000;
	private static final Scanner cin = new Scanner(System.in);

	public static void main(String[] args)
	{
		while(true)
		{
			int n = cin.nextInt();
			int a = cin.nextInt();
			int b = cin.nextInt();
			int c = cin.nextInt();
			int x = cin.nextInt();

			if(n == 0) { break; }

			int[] y = new int[n];

			for(int i = 0; i < n; i++)
			{
				y[i] = cin.nextInt();
			}

			int index = 0;
			int count = 0;

			while(count <= MAX_COUNT)
			{
				if(x == y[index])
				{
					++index;
					if(index == n) { break; }
				}

				x = (a * x + b) % c;
				++count;
			}

			if(count <= MAX_COUNT)
			{
				System.out.println(count);
			}
			else
			{
				System.out.println(  -1 );
			}
		}
	}
}