#include "bits/stdc++.h"
using namespace std;

#define DEBUG(x) cout<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cout<<#v<<":";for(int i=0;i<v.size();i++) cout<<" "<<v[i]; cout<<endl

typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
const int inf = 1000000001;
const ll INF = 1e18 * 2;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
int n, m;
int ans = 0;

int main() {
	int n, i, j;
	cin >> n;
	vi d(n);
	for (i = 0; i < n; i++) {
		cin >> d[i];
	}
	sort(d.begin(), d.end());
	reverse(d.begin(), d.end());
	int x, y;
	cin >> x >> y;
	x = abs(x);
	y = abs(y);
	for (i = 0; i < n; i++) {
		if (x + y == d[i]) {
			cout << 1 << endl;
			return 0;
		}
	}
	if ((x + y) % 2 == 0) {
		if (x + y <= 2 * d[0]) {
			cout << 2 << endl;
			return 2;
		}
		else {
			cout << -1 << endl;
			return -1;
		}
	}
	else {
		int d1 = d[0], d2 = -1;
		for (i = 1; i < n; i++) {
			if (d1 % 2 != d[i] % 2) {
				d2 = d[i];
				break;
			}
		}
		if (d2 == -1) {
			cout << -1 << endl;
			return 0;
		}
		if (x + y <= d1 + d2) {
			cout << 2 << endl;
			return 0;
		}
		else {
			cout << -1 << endl;
			return 0;
		}
	}
}