#include <bits/stdc++.h>
using namespace std;
const int maxn = 200005;
int n, l, x, y;
int a[maxn];
set<int> pos;
bool in(int x) { return x >= 0 && x <= l; }
int main() {
  scanf("%d%d%d%d", &n, &l, &x, &y);
  for (int i = 1, t; i <= n; i++) {
    scanf("%d", &a[i]);
    pos.insert(a[i]);
  }
  int repx = -1, repy = -1;
  for (int i = 1; i <= n; i++) {
    if (pos.count(a[i] - x)) repx = a[i];
    if (pos.count(a[i] - y)) repy = a[i];
  }
  if (repx != -1 && repy != -1) {
    printf("0\n");
    return 0;
  }
  if (repx != -1) {
    printf("1\n%d\n", y);
    return 0;
  }
  if (repy != -1) {
    printf("1\n%d\n", x);
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    if (pos.count(a[i] - x - y)) {
      printf("1\n%d\n", a[i] - x);
      return 0;
    }
    if (pos.count(a[i] - (y - x))) {
      if (in(a[i] + x)) {
        printf("1\n%d\n", a[i] + x);
        return 0;
      }
      if (in(a[i] - (y - x) - x)) {
        printf("1\n%d\n", a[i] - (y - x) - x);
        return 0;
      }
    }
  }
  printf("2\n%d %d\n", x, y);
  return 0;
}
