#include <bits/stdc++.h>
using namespace std;
set<int> arr;
int main() {
  int n, l, x, y;
  cin >> n >> l >> x >> y;
  for (int i = 0; i < n; i++) {
    int v;
    cin >> v;
    arr.insert(v);
  }
  bool f1, f2, f3, f4;
  int v3, v4;
  f1 = f2 = f3 = f4 = false;
  int res = 2147483647;
  for (auto v : arr) {
    f1 |= arr.count(v + x);
    f2 |= arr.count(v + y);
    if (arr.count(v + x + y)) {
      f3 = true;
      v3 = v + x;
    }
    if (arr.count(v + x - y)) {
      if (v - y >= 0) {
        f4 = true;
        v4 = v - y;
      } else if (v + x <= l) {
        f4 = true;
        v4 = v + x;
      }
    }
  }
  if (f1 && f2)
    cout << 0 << endl;
  else if (f1 || f2 || f3 || f4) {
    cout << 1 << endl;
    if (f1)
      cout << y << endl;
    else if (f2)
      cout << x << endl;
    else if (f3)
      cout << v3 << endl;
    else if (f4)
      cout << v4 << endl;
  } else
    cout << 2 << endl << x << " " << y << endl;
  return 0;
}
