#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse2")
using namespace std;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  std::cerr << name << " : " << arg1 << '\n';
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  std::cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
long long max(long long a, long long b) { return (a > b) ? a : b; }
long long min(long long a, long long b) { return (a < b) ? a : b; }
void amax(long long& a, long long b) { a = max(a, b) % 1000000007; }
void amin(long long& a, long long b) { a = min(a, b) % 1000000007; }
void inc(long long& a, long long b) { a = (a + b) % 1000000007; }
void dec(long long& a, long long b) { a = (a - b + 1000000007) % 1000000007; }
map<long long, long long> m;
long long l;
bool check(long long value) {
  if (value >= 0 && value <= l && m[value]) return true;
  return false;
}
bool c2(long long value) { return (value >= 0 && value <= l); }
long long solve() {
  long long n, x, y;
  cin >> n >> l >> x >> y;
  vector<long long> a(n);
  for (long long i = 0; i < n; ++i) cin >> a[i];
  for (long long i = 0; i < n; i++) m[a[i]]++;
  bool f1, f2;
  f1 = f2 = false;
  for (long long i = 0; i < n; i++) {
    if (check(a[i] - x) || check(a[i] + x)) f1 = true;
    if (check(a[i] - y) || check(a[i] + y)) f2 = true;
  }
  if (f1 && f2) {
    return cout << 0, 0;
  }
  if (f1) {
    return cout << 1 << '\n' << y, 0;
  }
  if (f2) return cout << 1 << '\n' << x, 0;
  for (long long i = 0; i < n; i++) {
    if (c2(a[i] - x)) {
      if (check(a[i] - x + y) || check(a[i] - x - y)) {
        return cout << 1 << '\n' << a[i] - x, 0;
      }
    }
    if (c2(a[i] + x)) {
      if (check(a[i] + x + y) || check(a[i] + x - y)) {
        return cout << 1 << '\n' << a[i] + x, 0;
      }
    }
  }
  return cout << 2 << '\n' << x << " " << y, 0;
  return 0;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t = 1;
  while (t--) {
    solve();
  }
}
