#include <bits/stdc++.h>
using namespace std;
int n, l, x, y, a[100005];
set<long long> st;
int main(int argc, char *argv[]) {
  ios_base::sync_with_stdio(false);
  cout.precision(10);
  cout << fixed;
  if (argc > 1 && fopen(argv[1], "r")) freopen(argv[1], "rt", stdin);
  cin >> n >> l >> x >> y;
  for (int i = 0; i < (int)(n); ++i) cin >> a[i], st.insert(a[i]);
  bool fx = 0, fy = 0;
  for (long long a1 : st) {
    if (st.count(a1 - x) || st.count(a1 + x)) {
      fx = 1;
      break;
    }
  }
  for (long long a1 : st) {
    if (st.count(a1 - y) || st.count(a1 + y)) {
      fy = 1;
      break;
    }
  }
  if (fx && fy)
    cout << 0 << endl;
  else if (fx)
    cout << 1 << endl << y << endl;
  else if (fy)
    cout << 1 << endl << x << endl;
  else {
    for (long long a1 : st) {
      long long a2 = a1 + x + y;
      if (st.count(a2)) {
        cout << 1 << endl << a1 + x << endl;
        return 0;
      }
      a2 = a1 - x + y;
      if (st.count(a2)) {
        if (a1 + y <= l) {
          cout << 1 << endl << a1 + y << endl;
          return 0;
        } else if (a1 - x >= 0) {
          cout << 1 << endl << a1 - x << endl;
          return 0;
        }
      }
      a2 = a1 + x - y;
      if (st.count(a2)) {
        if (a1 + x <= l) {
          cout << 1 << endl << a1 + x << endl;
          return 0;
        } else if (a1 - y >= 0) {
          cout << 1 << endl << a1 - y << endl;
          return 0;
        }
      }
      a2 = y - x;
      if (st.count(a2)) {
        cout << 1 << endl << y << endl;
        return 0;
      }
    }
    cout << 2 << endl << x << " " << y << endl;
  }
  return 0;
}
