#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, l, x, y;
  cin >> n >> l >> x >> y;
  long long arr[n];
  for (long long i = 0; i < n; ++i) cin >> arr[i];
  set<long long> stx, sty;
  bool bx = 0, by = 0;
  for (int i = 0; i < n; ++i) {
    bx |= binary_search(arr, arr + n, arr[i] - x) or
          binary_search(arr, arr + n, arr[i] + x);
    if (!bx) {
      if (arr[i] - x > 0) stx.insert(arr[i] - x);
      if (arr[i] + x < l) stx.insert(arr[i] + x);
    }
    by |= binary_search(arr, arr + n, arr[i] - y) or
          binary_search(arr, arr + n, arr[i] + y);
    if (!by) {
      if (arr[i] - y > 0) sty.insert(arr[i] - y);
      if (arr[i] + y < l) sty.insert(arr[i] + y);
    }
  }
  if (bx && by)
    cout << 0;
  else if (by)
    cout << 1 << '\n' << *stx.begin();
  else if (bx)
    cout << 1 << '\n' << *sty.begin();
  else {
    vector<long long> v(12345);
    v[0] = -1;
    set_intersection(stx.begin(), stx.end(), sty.begin(), sty.end(), v.begin());
    if (v[0] == -1)
      cout << 2 << '\n' << x << ' ' << y;
    else
      cout << 1 << '\n' << v[0];
  }
}
