import java.util.Arrays;
import java.util.HashSet;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n;
		long[] d;
		long x, y;
		n = sc.nextInt();
		d = new long[n];
		for (int i = 0; i < n; ++i)
			d[i] = sc.nextLong();
		x = sc.nextLong();
		y = sc.nextLong();
		System.out.println(solve(n, d, x, y));
	}

	static int solve(int n, long[] d, long x, long y) {
		x = Math.abs(x);
		y = Math.abs(y);
		if (x == 0 && y == 0) {
			return 0;
		}
		for (int i = 0; i < n; ++i) {
			if (d[i] == x + y) {
				return 1;
			}
		}
		HashSet<Long> set = new HashSet();
		for (int i = 0; i < n; ++i) {
			set.add(d[i]);
		}

		for (int i = 0; i < n; ++i) {
			if (!set.contains(x + y - d[i]) && !set.contains(x + y + d[i]))
				continue;
			return 2;
		}

		long maxoddD = 0, maxevenD = 0;
		for (int i = 0; i < n; ++i) {
			if (d[i] % 2 == 0)
				maxevenD = Math.max(maxevenD, d[i]);
			else
				maxoddD = Math.max(maxoddD, d[i]);
		}
		if ((x - y) % 2 == 0) {
			if (2 * Math.max(maxevenD, maxoddD) >= x + y) {
				return 2;
			}
		}
		return -1;

	}

	static void tr(Object... objects) {
		System.out.println(Arrays.deepToString(objects));
	}

}