using System;
using System.Linq;

public class Program
{
    static void Main()
    {
        string s = Console.ReadLine();
        int N = int.Parse(s);

        s = Console.ReadLine();
        var t = s.Split(' ');
        var D = new long[N];
        for (int i = 0; i < N; ++i) {
            D[i] = long.Parse(t[i]);
        }
        Array.Sort(D);

        s = Console.ReadLine();
        t = s.Split(' ');

        long x = long.Parse(t[0]);
        long y = long.Parse(t[1]);

        long X = Math.Abs(x + y);
        long Y = Math.Abs(x - y);
        long M = Math.Max(X, Y);

        if (x == 0 && y == 0) {
            Console.WriteLine(-1);
            return;
        }

        if (D.Contains(M)) {
            Console.WriteLine(1);
            return;
        } 

        for (int i = 0; i < N; ++i) {   
            int hi = i;
            int lo = 0;
            while (hi - lo > 1) {
                int mid = (hi + lo) / 2;
                if (D[i] - D[mid] >= M) {
                    lo = mid;
                } else {
                    hi = mid;
                }
            }

            if (lo == i) {
                lo -= 1;
            }

            if (lo >= 0 && D[i] - D[lo] <= M && M <= D[i] + D[lo]) {
                Console.WriteLine(2);
                return;
            }
        }

        for (int i = 0; i < N-1; ++i) {   
            int hi = i + 1;
            if (hi < N && D[hi] - D[i] <= M && M <= D[i] + D[hi]) {
                Console.WriteLine(2);
                return;
            }
        }

        Console.WriteLine(-1);
    }
}