#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
long long powmod(long long a, long long b) {
  long long res = 1;
  a %= mod;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
int n, l, x, y;
const int N = 101000;
int p[N];
set<int> st;
bool c1 = 0, c2 = 0;
bool check0() {
  for (int i = 0; i < n; i++) {
    if (st.count(p[i] + x) || st.count(p[i] - x)) c1 = 1;
    if (st.count(p[i] + y) || st.count(p[i] - y)) c2 = 1;
  }
  return c1 && c2;
}
bool check(int c) {
  if (st.count(c) || c < 0 || c > l) return 0;
  if ((c1 || st.count(c + x) || st.count(c - x)) &&
      (c2 || st.count(c + y) || st.count(c - y))) {
    puts("1");
    printf("%d\n", c);
    return 1;
  }
  return 0;
}
int main() {
  scanf("%d%d%d%d", &n, &l, &x, &y);
  for (int i = 0; i < n; i++) {
    scanf("%d", p + i);
    st.insert(p[i]);
  }
  if (check0()) {
    puts("0");
    return 0;
  }
  for (int i = 0; i < n; i++)
    if (check(p[i] + x) || check(p[i] - x) || check(p[i] + y) ||
        check(p[i] - y)) {
      return 0;
    }
  puts("2");
  printf("%d %d\n", x, y);
}
