#include <bits/stdc++.h>
using namespace std;
long long a, s, d, f, g, h, j, k, l, i, n, m;
set<long long> x, z, c, v;
int main() {
  cin >> n >> m >> k >> l;
  for (i = 0; i < n; i++) {
    scanf("%d", &a);
    x.insert(a + k);
    c.insert(a + l);
    s = x.size();
    x.insert(a);
    if (x.size() == s) {
      d = 1;
    }
    s = c.size();
    c.insert(a);
    if (c.size() == s) {
      f = 1;
    }
    s = z.size();
    z.insert(a + k);
    if (s == z.size())
      if (a + k < m)
        j = a + k;
      else if (a - l > 0)
        j = a - l;
    s = z.size();
    z.insert(a + l);
    if (s == z.size())
      if (a + l < m)
        j = a + l;
      else if (a - k > 0)
        j = a - k;
    s = v.size();
    v.insert(a + k);
    if (s == v.size() && a + k < m) j = a + k;
    s = v.size();
    v.insert(a - l);
    if (s == v.size() && a - l > 0) j = a - l;
  }
  if (d + f == 2)
    cout << 0;
  else if (d + f == 1) {
    cout << 1 << endl;
    if (d == 0)
      cout << k;
    else
      cout << l;
  } else if (j != 0)
    cout << 1 << endl << j;
  else
    cout << 2 << endl << k << " " << l;
}
