#include <bits/stdc++.h>
using namespace std;
int main() {
  map<long long, int> num;
  num.clear();
  long long n, l, x, y, curr;
  cin >> n >> l >> x >> y;
  int boy = 0, girl = 0;
  long long diff = y - x, sum = y + x, ans2 = -1, ans3 = -1;
  for (int i = 0; i <= n - 1; i++) {
    cin >> curr;
    if (boy & girl) continue;
    num[curr] = 1;
    if (curr >= x && num[curr - x]) girl = 1;
    if (curr >= y && num[curr - y]) boy = 1;
    if (ans2 == -1 && ans3 == -1) {
      if (curr >= diff && num[curr - diff]) {
        if (curr + x <= l)
          ans2 = curr + x;
        else if (curr - y >= 0)
          ans2 = curr - y;
      }
      if (curr >= sum && num[curr - sum]) ans3 = curr - sum;
    }
  }
  int ans = 2;
  if (boy) ans--;
  if (girl) ans--;
  if (ans == 0) {
    cout << ans << endl;
    return 0;
  } else if (ans == 1) {
    cout << "1\n";
    if (!boy) {
      cout << y;
      return 0;
    } else if (!girl) {
      cout << x;
      return 0;
    }
  } else {
    if (ans2 != -1) {
      cout << "1\n";
      cout << ans2;
      return 0;
    }
    if (ans3 != -1) {
      if (ans3 + x <= l) {
        cout << "1\n";
        cout << ans3 + x;
        return 0;
      }
    }
    cout << "2\n";
    cout << x << " " << y << endl;
  }
  return 0;
}
