#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
template <class T>
inline T tmin(T a, T b) {
  return (a < b) ? a : b;
}
template <class T>
inline T tmax(T a, T b) {
  return (a > b) ? a : b;
}
template <class T>
inline void add_max(T &a, T b) {
  if (b > a) a = b;
}
template <class T>
inline void add_min(T &a, T b) {
  if (b < a) a = b;
}
template <class T>
inline T tabs(T a) {
  return (a > 0) ? a : -a;
}
template <class T>
T gcd(T a, T b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
int main(int argc, char *argv[]) {
  ios_base::sync_with_stdio(false);
  int n, l, x, y;
  cin >> n >> l >> x >> y;
  vector<int> a(n);
  int ans = 2;
  bool tx = false, ty = false;
  for (int i = (0); i < (n); ++i) {
    cin >> a[i];
  }
  for (int i = (0); i < (n); ++i) {
    if (binary_search(a.begin(), a.end(), a[i] + x)) tx = true;
    if (binary_search(a.begin(), a.end(), a[i] + y)) ty = true;
  }
  if (tx && ty) {
    printf("%d\n", 0);
    return 0;
  }
  if (tx || ty) {
    if (!tx)
      printf("%d\n%d\n", 1, x);
    else
      printf("%d\n%d\n", 1, y);
    return 0;
  }
  for (int i = (0); i < (n); ++i) {
    if (a[i] >= x) {
      if (binary_search(a.begin(), a.end(), a[i] - x - y)) {
        printf("%d\n%d\n", 1, a[i] - x);
        return 0;
      }
      if (binary_search(a.begin(), a.end(), a[i] - x + y)) {
        printf("%d\n%d\n", 1, a[i] - x);
        return 0;
      }
    }
    if (a[i] + x <= l) {
      if (binary_search(a.begin(), a.end(), a[i] + x - y)) {
        printf("%d\n%d\n", 1, a[i] + x);
        return 0;
      }
      if (binary_search(a.begin(), a.end(), a[i] + x + y)) {
        printf("%d\n%d\n", 1, a[i] + x);
        return 0;
      }
    }
  }
  printf("%d\n%d %d\n", 2, x, y);
  return 0;
}
