#include <bits/stdc++.h>

using namespace std;

const int MAX = 1e5 + 10;
int n;
long long d[MAX], x, y;

int main() {
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%lld", d + i);
  }
  n++;
  scanf("%lld%lld", &x, &y);
  x = llabs(x);
  y = llabs(y);
  if (x == 0 && y == 0) {
    cout << 0 << endl;
    return 0;
  }
  long long xy = x + y;
  for (int i = 0; i < n; i++) {
    if (d[i] == xy) {
      cout << 1 << endl;
      return 0;
    }
  }
  sort(d, d + n);
  if (xy % 2) {
    long long now[2];
    now[0] = now[1] = -1;
    for (int i = 0; i < n; i++) {
      now[d[i] % 2] = d[i];
      if (now[0] != -1 && now[1] != -1) {
        if (llabs(now[0] - now[1]) <= xy && xy <= now[0] + now[1]) {
          cout << 2 << endl;
          return 0;
        }
      }
    }
  } else {
    if (xy <= d[n - 1] * 2) {
      cout << 2 << endl;
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}