#include <bits/stdc++.h>

using namespace std;

#define int long long

signed main()
{
  int N, D[100000], X, Y;

  cin >> N;

  for(int i = 0; i < N; i++) {
    cin >> D[i];
  }

  cin >> X >> Y;

  if(X == 0 && Y == 0) {
    cout << 0 << endl;
    return (0);
  }

  int F = abs(X) + abs(Y);
  for(int i = 0; i < N; i++) {
    if(F == D[i]) {
      cout << 1 << endl;
      return (0);
    }
  }

  sort(D, D + N);
  vector< int > push;
  int S = X + Y, T = X - Y;
  for(int i = 0; i < N; i++) {
    push.emplace_back(max({D[i] - S, -D[i] + T, D[i] - T, -D[i] + T}));
  }
  for(int i = 0; i < push.size(); i++) {
    if(binary_search(D, D + N, push[i])) {
      cout << 2 << endl;
      return (0);
    }
  }
  cout << -1 << endl;
}