#include <bits/stdc++.h>
using namespace std;
bool binary_search(int a[], int val, int start, int end) {
  while (start <= end) {
    int mid = (start + end) / 2;
    if (a[mid] == val) return true;
    if (a[mid] < val)
      start = mid + 1;
    else
      end = mid - 1;
  }
  return false;
}
int main() {
  int n, l, x, y;
  cin >> n >> l >> x >> y;
  int *a = new int[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  bool flagx = 0;
  for (int i = 0; i < n; i++) {
    flagx = binary_search(a, a[i] + x, i + 1, n - 1);
    if (flagx) break;
  }
  bool flagy = 0;
  for (int i = 0; i < n; i++) {
    flagy = binary_search(a, a[i] + y, i + 1, n - 1);
    if (flagy) break;
  }
  if (flagx == 0 && flagy == 0) {
    bool flag = false;
    for (int i = 0; i < n; i++) {
      flag = binary_search(a, a[i] + x + y, i + 1, n - 1);
      if (flag) {
        cout << 1 << endl << a[i] + x << endl;
        return 0;
      }
    }
    for (int i = 0; i < n; i++) {
      int val = a[i] + x - y;
      flag = binary_search(a, val, 0, n - 1);
      if (flag && a[i] + x <= l) {
        cout << 1 << endl << a[i] + x << endl;
        return 0;
      }
    }
    for (int i = 0; i < n; i++) {
      int val = a[i] + y - x;
      flag = binary_search(a, val, 0, n - 1);
      if (flag && a[i] - x >= 0) {
        cout << 1 << endl << a[i] - x << endl;
        return 0;
      }
    }
    cout << 2 << endl;
    cout << x << " " << y << endl;
    return 0;
  }
  if (flagx == 0) {
    cout << 1 << endl;
    cout << x << endl;
    return 0;
  }
  if (flagy == 0) {
    cout << 1 << endl << y << endl;
    return 0;
  }
  cout << 0 << endl;
  return 0;
}
