#include <bits/stdc++.h>
using namespace std;
set<int> S;
int a[200000], n, l, x, y, now;
bool fx, fy;
int main() {
  scanf("%d%d%d%d", &n, &l, &x, &y);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
    S.insert(a[i]);
  }
  for (int i = 1; i <= n; i++) {
    now = a[i] - x;
    if (S.find(now) != S.end()) {
      fx = true;
      break;
    }
    now = a[i] + x;
    if (S.find(now) != S.end()) {
      fx = true;
      break;
    }
  }
  for (int i = 1; i <= n; i++) {
    now = a[i] - y;
    if (S.find(now) != S.end()) {
      fy = true;
      break;
    }
    now = a[i] + y;
    if (S.find(now) != S.end()) {
      fy = true;
      break;
    }
  }
  if (fx && fy) {
    puts("0");
    return 0;
  }
  if (fx && !fy) {
    puts("1");
    printf("%d\n", y);
    return 0;
  }
  if (!fx && fy) {
    puts("1");
    printf("%d\n", x);
    return 0;
  }
  if (!fx && !fy) {
    for (int i = 1; i <= n; i++) {
      now = a[i] + x + y;
      if (S.find(now) != S.end()) {
        puts("1");
        printf("%d\n", a[i] + x);
        return 0;
      }
      now = a[i] - x - y;
      if (S.find(now) != S.end()) {
        puts("1");
        printf("%d\n", a[i] - x);
        return 0;
      }
      now = a[i] + x - y;
      if (S.find(now) != S.end()) {
        if (a[i] + x <= l) {
          puts("1");
          printf("%d\n", a[i] + x);
          return 0;
        }
        if (a[i] - y >= 0) {
          puts("1");
          printf("%d\n", a[i] - y);
        }
      }
      now = a[i] - x + y;
      if (S.find(now) != S.end()) {
        if (a[i] - x >= 0) {
          puts("1");
          printf("%d\n", a[i] - x);
          return 0;
        }
        if (a[i] + y <= l) {
          puts("1");
          printf("%d\n", a[i] + y);
          return 0;
        }
      }
    }
    puts("2");
    printf("%d %d\n", x, y);
    return 0;
  }
}
