#include <bits/stdc++.h>
using namespace std;
int n, l, x, y;
int a[100000];
int fnd1(int f) {
  int l = 0;
  for (int r = 0; r < n; r++) {
    while (a[l] + f < a[r] && l < n) l++;
    if (a[l] + f == a[r]) return l;
  }
  return -1;
}
int fnd2(int f) {
  int r = n - 1;
  for (int l = n - 1; l >= 0; l--) {
    while (a[l] + f < a[r] && r >= 0) r--;
    if (a[l] + f == a[r]) return l;
  }
  return -1;
}
int main() {
  ios::sync_with_stdio(false);
  cin >> n >> l >> x >> y;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  bool p, q;
  p = q = 0;
  p = (fnd1(x) != -1);
  q = (fnd1(y) != -1);
  if (p && q)
    cout << 0 << endl;
  else {
    if (p)
      cout << 1 << endl << y << endl;
    else if (q)
      cout << 1 << endl << x << endl;
    else {
      int c;
      c = fnd1(x + y);
      if (c != -1) {
        cout << 1 << endl << a[c] + x << endl;
        return 0;
      }
      c = fnd1(y - x);
      if (c != -1 && a[c] + y <= l) {
        cout << 1 << endl << a[c] + y << endl;
        return 0;
      }
      c = fnd2(y - x);
      if (c != -1 && a[c] - x >= 0) {
        cout << 1 << endl << a[c] - x << endl;
      } else
        cout << 2 << endl << x << " " << y << endl;
    }
  }
  return 0;
}
