#include <bits/stdc++.h>
using namespace std;
template <class T>
bool umin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool umax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
int arr[100009];
map<int, int> pm, hs;
int main() {
  int n, l, x, y;
  scanf("%d%d%d%d", &n, &l, &x, &y);
  for (int i = 1; i <= n; i++) scanf("%d", arr + i), pm[arr[i]] = 1;
  int dx = 0, dy = 0;
  for (int i = 1; i <= n; i++) {
    if (pm[arr[i] + x] or pm[arr[i] - x]) dx = 1;
    if (pm[arr[i] + y] or pm[arr[i] - y]) dy = 1;
    if (arr[i] + x <= l) hs[arr[i] + x] = 1;
    if (arr[i] - x >= 0) hs[arr[i] - x] = 1;
  }
  if (dx or dy) {
    if (dx and dy)
      printf("0\n");
    else if (dx)
      printf("1\n%d\n", y);
    else
      printf("1\n%d\n", x);
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    if (hs[arr[i] + y] or hs[arr[i] - y]) {
      if (hs[arr[i] + y] and arr[i] + y <= l) {
        printf("1\n%d\n", arr[i] + y);
        return 0;
      } else if (hs[arr[i] - y] and arr[i] - y >= 0) {
        printf("1\n%d\n", arr[i] - y);
        return 0;
      }
    }
  }
  printf("2\n%d %d\n", x, y);
  return 0;
}
