#include <iostream>
#include <iomanip>
#include <cstring>
#include <algorithm> 
#include <math.h>
#include <queue>
#include <functional>
#include <map>
#include <vector>
#include <string>
using namespace std;
typedef long long ll;

ll n, x, y,d[100005];
int main(void){
    cin >> n;
    ll Min = 1000000005, Max = -1;
    for (int i = 0; i < n; i++){
        cin >> d[i];
        Min = min(Min, d[i]); Max = max(Max, d[i]);
    }
    cin >> x >> y;
    x = max(x, -x);
    y = max(y, -y);
    
    for (int i = 0; i < n; i++){
        if (x + y == d[i]){
            cout << 1 << endl;
            return 0;
        }
    }

    if (x + y < Min * 2 || x + y > Max * 2) cout << -1 << endl;
    else cout << 2 << endl;

}