#include <bits/stdc++.h>
using namespace std;
void query() {
  long long n, l, x, y;
  cin >> n >> l >> x >> y;
  long long a[n];
  map<long long, long long> m;
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
    m[a[i]] = 1;
  }
  bool f1 = false, f2 = false;
  for (long long i = 1; i < n; i++) {
    f1 |= (m.find(a[i] - x) != m.end());
    f2 |= (m.find(a[i] - y) != m.end());
  }
  long long tt = (!f1) + (!f2);
  if (tt == 0) {
    cout << "0\n";
  } else if (tt == 1) {
    cout << "1\n";
    if (f1) cout << y << "\n";
    if (f2) cout << x << "\n";
  } else {
    for (long long i = 0; i < n; i++) {
      if (a[i] - x >= 0 && (m.find(a[i] - x - y) != m.end() ||
                            m.find(a[i] - x + y) != m.end())) {
        cout << "1\n";
        cout << a[i] - x;
        return;
      }
      if (a[i] + x <= l && (m.find(a[i] + x - y) != m.end() ||
                            m.find(a[i] + x + y) != m.end())) {
        cout << "1\n";
        cout << a[i] + x;
        return;
      }
      if (a[i] - y >= 0 && (m.find(a[i] - y - x) != m.end() ||
                            m.find(a[i] - y + x) != m.end())) {
        cout << "1\n";
        cout << a[i] - y;
        return;
      }
      if (a[i] + y <= l && (m.find(a[i] + y - x) != m.end() ||
                            m.find(a[i] + y + x) != m.end())) {
        cout << "1\n";
        cout << a[i] + y;
        return;
      }
    }
    cout << 2 << "\n";
    cout << x << " " << y << "\n";
  }
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long t = 1;
  while (t--) {
    query();
  }
}
