#include <bits/stdc++.h>
using namespace std;
const long long N = 2e5 + 5;
const long long mod = 1e9;
#pragma GCC optimize("-O2")
const long long INF = 10000000;
long long getIInput() {
  cout.flush();
  long long x;
  cin >> x;
  return x;
}
void flash() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cout.setf(ios::fixed);
  cout.setf(ios::showpoint);
  cout.precision(9);
}
void solve();
int32_t main() {
  flash();
  long long t;
  t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
void solve() {
  long long n, l, x, y;
  cin >> n >> l >> x >> y;
  stack<long long> st, ff;
  st.push(x);
  st.push(y);
  long long a[n];
  map<long long, long long> present;
  for (long long i = 0; i < n; i++) {
    cin >> a[i];
    present[a[i]] = 1;
  }
  for (long long cnt = 0; cnt < 2; cnt++) {
    bool found = 0;
    for (long long i = 0; i < n; i++) {
      long long x = st.top();
      if (present.find(a[i] + x) != present.end()) {
        found = 1;
        break;
      }
    }
    if (found == 0) {
      ff.push(st.top());
    }
    st.pop();
  }
  if (ff.size() == 0) {
    cout << "0\n";
    return;
  }
  if (ff.size() == 1) {
    cout << 1 << "\n";
    cout << ff.top() << "\n";
    return;
  }
  long long z = x + y;
  for (long long i = 0; i < n; i++) {
    if (present.find(z + a[i]) != present.end()) {
      cout << "1\n";
      cout << a[i] + x << "\n";
      return;
    }
    if (a[i] + x >= 0 && a[i] + x <= l &&
        present.find(a[i] + x - y) != present.end()) {
      cout << "1\n";
      cout << a[i] + x << "\n";
      return;
    }
    if (a[i] - x >= 0 && a[i] - x <= l &&
        present.find(a[i] - x + y) != present.end()) {
      cout << "1\n";
      cout << a[i] - x << "\n";
      return;
    }
    if (a[i] - y >= 0 && a[i] - y <= l &&
        present.find(a[i] + x - y) != present.end()) {
      cout << "1\n";
      cout << a[i] - y << "\n";
      return;
    }
    if (a[i] + y >= 0 && a[i] + y <= l &&
        present.find(a[i] - x + y) != present.end()) {
      cout << "1\n";
      cout << a[i] + y << "\n";
      return;
    }
  }
  cout << 2 << "\n";
  cout << x << " " << y << "\n";
  return;
}
