#include <bits/stdc++.h>
using namespace std;
const long long N = 100011;
vector<long long> v;
long long dist[2];
bool ok[2];
bool puede(long long l, long long n) {
  for (long long i = 0; i < n; i++) {
    long long pos = lower_bound(v.begin(), v.end(), v[i] + l) - v.begin();
    if (pos == n) break;
    if (v[pos] == v[i] + l) {
      return true;
    }
  }
  return false;
}
bool puede2(long long l, long long n) {
  long long pos = lower_bound(v.begin(), v.end(), l) - v.begin();
  if (pos == n) return false;
  if (v[pos] == l) {
    return true;
  }
  return false;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.precision(10);
  cout << fixed;
  long long n, l, q;
  cin >> n >> l >> dist[0] >> dist[1];
  for (long long i = 0; i < n; i++) {
    cin >> q;
    v.push_back(q);
  }
  for (long long i = 0; i < 2; i++) {
    ok[i] = puede(dist[i], n);
  }
  if (ok[0] && ok[1]) {
    cout << 0 << endl;
    return 0;
  }
  if (ok[0] || ok[1]) {
    cout << 1 << endl;
    if (ok[0]) {
      cout << dist[1] << endl;
    } else {
      cout << dist[0] << endl;
    }
    return 0;
  }
  for (long long i = 0; i < n; i++) {
    long long pos =
        lower_bound(v.begin(), v.end(), v[i] + dist[1] + dist[0]) - v.begin();
    if (pos == n) break;
    if (v[pos] == v[i] + dist[1] + dist[0]) {
      cout << 1 << endl;
      cout << v[i] + dist[0] << endl;
      return 0;
    }
  }
  for (long long i = 0; i < n; i++) {
    if (0 <= v[i] - dist[0] && puede2(v[i] - dist[0] + dist[1], n)) {
      cout << 1 << endl;
      cout << v[i] - dist[0] << endl;
      return 0;
    }
    if (0 <= v[i] - dist[1] && puede2(v[i] - dist[1] + dist[0], n)) {
      cout << 1 << endl;
      cout << v[i] - dist[1] << endl;
      return 0;
    }
    if (v[i] + dist[1] <= v[n - 1] && puede2(v[i] - dist[0] + dist[1], n)) {
      cout << 1 << endl;
      cout << v[i] + dist[1] << endl;
      return 0;
    }
    if (v[i] + dist[0] <= v[n - 1] && puede2(v[i] - dist[1] + dist[0], n)) {
      cout << 1 << endl;
      cout << v[i] + dist[0] << endl;
      return 0;
    }
  }
  cout << 2 << endl;
  cout << dist[0] << " ";
  cout << dist[1] << endl;
  return 0;
}
