#include <bits/stdc++.h>
using namespace std;
const int maxn = 100005;
set<int> st;
int n, x, y, l, d[maxn], solvex, solvey;
int main() {
  scanf("%d%d%d%d", &n, &l, &x, &y);
  solvex = solvey = false;
  for (int i = 1; i <= n; i++) {
    scanf("%d", d + i);
    st.insert(d[i]);
  }
  for (int i = 1; i <= n; i++) {
    if (st.count(d[i] - x) || st.count(d[i] + x)) {
      solvex = true;
    }
    if (st.count(d[i] - y) || st.count(d[i] + y)) {
      solvey = true;
    }
  }
  if (solvex && !solvey) {
    printf("1\n%d\n", y);
    return 0;
  }
  if (!solvex && solvey) {
    printf("1\n%d\n", x);
    return 0;
  }
  if (solvex && solvey) {
    puts("0");
    return 0;
  }
  if (x > y) swap(x, y);
  for (int i = 1; i <= n; i++) {
    if (st.count(d[i] + x + y)) {
      printf("1\n%d\n", d[i] + x);
      return 0;
    }
    if (st.count(d[i] - x - y)) {
      printf("1\n%d\n", d[i] - x);
      return 0;
    }
    if (d[i] >= x && st.count(d[i] + y - x)) {
      printf("1\n%d\n", d[i] - x);
      return 0;
    }
    if (d[i] + x <= l && st.count(d[i] + x - y)) {
      printf("1\n%d\n", d[i] + x);
      return 0;
    }
  }
  printf("2\n%d %d\n", x, y);
  return 0;
}
