#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
long long dx[] = {-1, 0, 1, 0};
long long dy[] = {0, -1, 0, 1};
long long msum(long long a, long long b, long long m) {
  return (a % m + b % m) % m;
}
long long msub(long long a, long long b, long long m) {
  return (a % m - b % m) % m;
}
long long mpro(long long a, long long b, long long m) {
  return ((a % m) * (b % m)) % m;
}
long long m_m(long long a, long long b, long long m);
long long fxp(long long a, long long b, long long m);
void swap(long long &a, long long &b) {
  long long t = a;
  a = b;
  b = t;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t--) {
    long long n, l, x, y, i, j;
    cin >> n >> l >> x >> y;
    vector<long long> v;
    vector<long long> res;
    map<long long, long long> m;
    for (i = 0; i < n; i++) {
      long long tm;
      cin >> tm;
      v.push_back(tm);
      m[tm] = 1;
    }
    long long check_x = 0, check_y = 0, res1 = -1, res2 = -1;
    for (i = 0; i < n; i++) {
      if (m[v[i] + x]) check_x = 1;
      if (m[v[i] + y]) check_y = 1;
      if (m[v[i] + y + x] && res1 == -1) {
        res1 = v[i] + y;
      }
      if (m[v[i] + y - x] && res1 == -1) {
        if (v[i] + y <= l) res1 = v[i] + y;
        if (v[i] - x >= 0) res1 = v[i] - x;
      }
    }
    if (check_x && check_y)
      cout << 0;
    else if (check_x)
      cout << 1 << "\n" << y;
    else if (check_y)
      cout << 1 << "\n" << x;
    else if (res1 != -1)
      cout << 1 << "\n" << res1;
    else {
      cout << 2 << "\n";
      cout << x << " " << y;
    }
    cout << "\n";
  }
  return 0;
}
long long fxp(long long a, long long b, long long m) {
  if (b == 0) return 1;
  if (b % 2 == 0) return fxp(m_m(a, a, m), b / 2, m);
  return m_m(fxp(a, b - 1, m), a, m);
}
long long m_m(long long a, long long b, long long m) {
  long long res = 0;
  a = a % m;
  while (b) {
    if (b & 1) {
      res += a;
      res = res % m;
    }
    a = (a * 2) % m;
    b = b / 2;
  }
  return res;
}
