#include <bits/stdc++.h>
using namespace std;
const int maxn = 100050;
int n, l, x, y, a[maxn];
map<int, int> q;
int main() {
  int i, j;
  bool z1 = 0, z2 = 0;
  scanf("%d%d%d%d\n", &n, &l, &x, &y);
  for (i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    q[a[i]] = 1;
    if (q.count(a[i] - x)) z1 = 1;
    if (q.count(a[i] - y)) z2 = 1;
  }
  if (z1 && z2)
    printf("0\n");
  else if (z1)
    printf("1\n%d\n", y);
  else if (z2)
    printf("1\n%d\n", x);
  else {
    for (i = 1; i <= n; i++)
      if (q[a[i] + x - y]) {
        if (a[i] + x <= l) {
          printf("1\n%d\n", a[i] + x);
          return 0;
        }
        if (a[i] - y >= 0) {
          printf("1\n%d\n", a[i] - y);
          return 0;
        }
      } else if (q[a[i] - x - y]) {
        printf("1\n%d\n", a[i] - x);
        return 0;
      }
    printf("2\n%d %d\n", x, y);
  }
  return 0;
}
