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 = sc.nextInt();
		long[] d = new long[n];
		for (int i = 0; i < n; ++i) {
			d[i] = sc.nextLong();
		}
		int x = sc.nextInt();
		int y = sc.nextInt();
		x = Math.abs(x);
		y = Math.abs(y);
		if (x == 0 && y == 0) {
			System.out.println(0);
			return;
		}
		for (int i = 0; i < n; ++i) {
			if (d[i] == x + y) {
				System.out.println(1);
				return;
			}
		}
		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;
			System.out.println(2);
			return;
		}
		System.out.println(-1);

	}

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

}