#include <bits/stdc++.h>
using namespace std;
map<long long, bool> mp;
long long a[100010];
int main() {
  long long n, l, x, y;
  cin >> n >> l >> x >> y;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    mp[a[i]] = 1;
  }
  int j = 0;
  bool isx = 0;
  for (int i = 0; i < n; i++) {
    while (a[j] - a[i] < x && j < n - 1) j++;
    if (a[j] - a[i] == x) isx = 1;
  }
  j = 0;
  bool isy = 0;
  for (int i = 0; i < n; i++) {
    while (a[j] - a[i] < y && j < n - 1) j++;
    if (a[j] - a[i] == y) isy = 1;
  }
  if (isx && isy) {
    cout << 0 << endl;
    return 0;
  }
  if (isx && !isy) {
    cout << 1 << endl;
    cout << y << endl;
    return 0;
  }
  if (!isx && isy) {
    cout << 1 << endl;
    cout << x << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    long long tmp = a[i] - x;
    if (tmp >= 0) {
      if (mp[tmp - y] || mp[tmp + y]) {
        cout << 1 << endl;
        cout << tmp << endl;
        return 0;
      }
    }
    tmp = a[i] + x;
    if (tmp <= l) {
      if (mp[tmp - y] || mp[tmp + y]) {
        cout << 1 << endl;
        cout << tmp << endl;
        return 0;
      }
    }
  }
  cout << 2 << endl;
  cout << x << " " << y << endl;
  return 0;
}
