#include <bits/stdc++.h>
using namespace std;
int n;
long long l, x, y;
vector<long long> val;
int main() {
  scanf("%d %lld %lld %lld", &n, &l, &x, &y);
  for (int i = 0; i < n; i++) {
    long long a;
    scanf("%lld", &a);
    val.push_back(a);
  }
  bool ex = 0, ey = 0;
  for (int i = 0; i < n; i++) {
    if (binary_search(val.begin(), val.end(), val[i] + x)) {
      ex = true;
    }
    if (binary_search(val.begin(), val.end(), val[i] + y)) {
      ey = true;
    }
  }
  if (ex && ey) {
    puts("0");
    return 0;
  }
  long long a[4];
  bool ok = false;
  long long res = -1;
  for (int i = 0; i < n && !ok; i++) {
    a[0] = val[i] - x;
    a[1] = val[i] - y;
    a[2] = val[i] + x;
    a[3] = val[i] + y;
    for (int j = 0; j < 4 && !ok; j++) {
      if (!(0 <= a[j] && a[j] <= l)) continue;
      if (j % 2 == 0) {
        if (binary_search(val.begin(), val.end(), a[j] - y) || ey) {
          ok = true;
          res = a[j];
        }
        if (binary_search(val.begin(), val.end(), a[j] + y) || ey) {
          ok = true;
          res = a[j];
        }
      } else {
        if (binary_search(val.begin(), val.end(), a[j] - x) || ex) {
          ok = true;
          res = a[j];
        }
        if (binary_search(val.begin(), val.end(), a[j] + x) || ex) {
          ok = true;
          res = a[j];
        }
      }
    }
  }
  if (ok) {
    printf("1\n%lld\n", res);
    return 0;
  } else {
    printf("2\n%lld %lld\n", x, y);
    return 0;
  }
}
