#include <bits/stdc++.h>
const long long N = 500005;
const long long mod = 1e9 + 7;
using namespace std;
void solve() {
  long long n, l, x, y;
  cin >> n >> l >> x >> y;
  long long arr[n];
  set<long long> finds;
  for (long long i = 0; i < n; i++) {
    cin >> arr[i];
    finds.insert(arr[i]);
  }
  bool gf = 0, bf = 0;
  for (long long i = 0; i < n; i++) {
    if (x + arr[i] <= l and finds.find(x + arr[i]) != finds.end()) {
      gf = 1;
      break;
    }
    if (arr[i] - x >= 0 and finds.find(arr[i] - x) != finds.end()) {
      gf = 1;
      break;
    }
  }
  for (long long i = 0; i < n; i++) {
    if (y + arr[i] <= l and finds.find(y + arr[i]) != finds.end()) {
      bf = 1;
      break;
    }
    if (arr[i] - y >= 0 and finds.find(arr[i] - y) != finds.end()) {
      bf = 1;
      break;
    }
  }
  if (gf and bf) {
    cout << "0\n";
    return;
  }
  if (gf) {
    cout << "1\n" << y << endl;
    return;
  }
  if (bf) {
    cout << "1\n" << x << endl;
    return;
  }
  for (long long i = 0; i < n; i++) {
    long long ele = arr[i] + x;
    if ((ele >= 0 and ele <= l) and (finds.find(ele - y) != finds.end() or
                                     finds.find(ele + y) != finds.end())) {
      cout << "1\n" << ele << endl;
      return;
    }
    ele = arr[i] - x;
    if ((ele >= 0 and ele <= l) and (finds.find(ele - y) != finds.end() or
                                     finds.find(ele + y) != finds.end())) {
      cout << "1\n" << ele << endl;
      return;
    }
  }
  cout << "2\n" << x << " " << y << endl;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long T = 1;
  while (T--) {
    solve();
  }
  return 0;
}
