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 count = 0;
			int last_count = -1;

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

				while(!(x == y && last_count != count) && count <= MAX_COUNT)
				{
					x = (a * x + b) % c;
					++count;
				}

				last_count = count;
			}

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