#include <bits/stdc++.h>
using namespace std;
const int mod = 1000000007;
const long long inf = 1000000000000;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, l, x, y;
  cin >> n >> l >> x >> y;
  vector<int> vm;
  map<int, int> mp;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    if (mp[x] == 0) {
      vm.push_back(x);
      mp[x]++;
    }
  }
  if (mp[0] == 0) {
    vm.push_back(0);
    mp[0] = 1;
  }
  if (mp[l] == 0) {
    vm.push_back(l);
    mp[l] = 1;
  }
  sort(vm.begin(), vm.end());
  int cnt = 0;
  map<int, int> mp2;
  for (int i = 0; i < vm.size(); i++) {
    int cur = vm[i];
    if (mp[cur - x] == 1 && mp2[x] == 0) {
      cnt++;
      mp2[x] = 1;
    }
    if (mp[cur - y] == 1 && mp2[y] == 0) {
      cnt++;
      mp2[y] = 1;
    }
  }
  if (cnt == 2) {
    cout << "0" << '\n';
    return 0;
  } else if (cnt == 1) {
    cout << "1" << '\n';
    if (mp2[x] == 0) {
      cout << x << '\n';
    } else
      cout << y << '\n';
    return 0;
  } else if (cnt == 0) {
    for (int i = 0; i < vm.size(); i++) {
      int cur = vm[i];
      if (cur - x >= 0 && (mp[cur - x + y] == 1 || mp[cur - x - y] == 1)) {
        cout << "1" << '\n';
        cout << cur - x << '\n';
        return 0;
      } else if (cur + x <= l &&
                 (mp[cur + x - y] == 1 || mp[cur + x + y] == 1)) {
        cout << "1" << '\n';
        cout << cur + x << '\n';
        return 0;
      }
      if (cur - y >= 0 && (mp[cur - y + x] == 1 || mp[cur - y - x] == 1)) {
        cout << "1" << '\n';
        cout << cur - y << '\n';
        return 0;
      } else if (cur + y <= l &&
                 (mp[cur + y - x] == 1 || mp[cur + y + x] == 1)) {
        cout << "1" << '\n';
        cout << cur + y << '\n';
        return 0;
      }
    }
  }
  cout << "2" << '\n';
  cout << x << " " << y << '\n';
  return 0;
}
