#include <bits/stdc++.h>
using namespace std;
int n, i, flaga, flagb, sc;
long long l, x, y, ans;
long long a[200000];
map<long long, int> bo;
int main() {
  scanf("%d %lld %lld %lld", &n, &l, &x, &y);
  for (i = 0; i < n; i++) {
    scanf("%d", &a[i]);
    bo[a[i]] = 1;
  }
  for (i = 0; i < n; i++) {
    if (bo[a[i] + x] == 1) flaga = 1;
    if (bo[a[i] + y] == 1) flagb = 1;
  }
  if (flaga == 1 && flagb == 1) printf("0\n");
  if (flaga == 1 && flagb == 0) {
    printf("1\n%lld\n", y);
  }
  if (flagb == 1 && flaga == 0) {
    printf("1\n%lld\n", x);
  }
  if (flaga == 0 && flagb == 0) {
    for (i = 0; i < n; i++) {
      if (bo[a[i] - x + y] == 1 && a[i] - x >= 0) {
        printf("1\n%lld\n", a[i] - x);
        sc = 1;
        break;
      }
      if (bo[a[i] + x - y] == 1 && a[i] + x <= l) {
        printf("1\n%lld\n", a[i] + x);
        sc = 1;
        break;
      }
      if (bo[a[i] - y + x] == 1 && a[i] - y >= l) {
        printf("1\n%lld\n", a[i] - y);
        sc = 1;
        break;
      }
      if (bo[a[i] + y - x] == 1 && a[i] + y <= l) {
        printf("1\n%lld\n", a[i] + y);
        sc = 1;
        break;
      }
      if (bo[a[i] + x + y] == 1) {
        printf("1\n%lld\n", a[i] + x);
        sc = 1;
        break;
      }
      if (bo[a[i] - x - y] == 1) {
        printf("1\n%lld\n", a[i] - x);
        sc = 1;
        break;
      }
    }
    if (sc != 1) printf("2\n%lld %lld\n", x, y);
  }
  return 0;
}
