#include <bits/stdc++.h>
using namespace std;
int n, a[1000000 + 100], l, x, y;
int temp3, temp4;
map<int, int> mapa;
int solve() {
  for (int i = 1; i <= n; i++) {
    int curr = a[i] + x + y;
    int curr2 = a[i] + x - y;
    int curr3 = a[i] - x + y;
    int curr4 = a[i] - x - y;
    if (mapa[curr] && curr <= l && curr >= 0 && curr - y >= 0 && curr - y <= l)
      return curr - y;
    if (mapa[curr2] && curr2 <= l && curr2 >= 0 && curr2 + y >= 0 &&
        curr2 + y <= l)
      return curr2 + y;
    if (mapa[curr3] && curr3 <= l && curr3 >= 0 && curr3 - y >= 0 &&
        curr3 - y <= l)
      return curr3 - y;
    if (mapa[curr4] && curr4 <= l && curr4 >= 0 && curr4 + y >= 0 &&
        curr4 - y <= l)
      return curr4 + y;
    curr = a[i] + y + x;
    curr2 = a[i] + y - x;
    curr3 = a[i] - y + x;
    curr4 = a[i] - y - x;
    if (mapa[curr] && curr <= l && curr >= 0 && curr - x >= 0 && curr - x <= l)
      return curr - x;
    if (mapa[curr2] && curr2 <= l && curr2 >= 0 && curr2 + x >= 0 &&
        curr2 + x <= l)
      return curr2 + x;
    if (mapa[curr3] && curr3 <= l && curr3 >= 0 && curr3 - x >= 0 &&
        curr3 - x <= l)
      return curr3 - x;
    if (mapa[curr4] && curr4 <= l && curr4 >= 0 && curr4 + x >= 0 &&
        curr4 + x <= l)
      return curr4 + x;
  }
  return -1;
}
int main() {
  cin >> n >> l >> x >> y;
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]), mapa[a[i]]++;
  if (mapa[x] && mapa[y]) {
    cout << 0 << endl;
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    int curr = a[i] + x;
    if (curr <= l && mapa[curr] && curr >= 0) temp3 = 1;
    curr = a[i] - x;
    if (curr >= 0 && mapa[curr] && curr >= 0) temp3 = 1;
    curr = a[i] + y;
    if (curr <= l && mapa[curr] && curr >= 0) temp4 = 1;
    curr = a[i] - y;
    if (curr >= 0 && mapa[curr] && curr >= 0) temp4 = 1;
  }
  if (temp3 && temp4) {
    cout << 0 << endl;
    return 0;
  }
  if (temp3 && !temp4) {
    cout << 1 << endl << l - y << endl;
    return 0;
  }
  if (temp4 && !temp3) {
    cout << 1 << endl << l - x << endl;
    return 0;
  }
  int cnt = solve();
  if (cnt == -1) {
    cout << 2 << endl << x << ' ' << y << endl;
    return 0;
  }
  cout << 1 << endl << cnt << endl;
  return 0;
}
