#include <bits/stdc++.h>
using namespace std;
template <typename F, typename S>
ostream &operator<<(ostream &os, const pair<F, S> &p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "{";
  typename vector<T>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "}";
}
template <typename T>
ostream &operator<<(ostream &os, const set<T> &v) {
  os << "[";
  typename set<T>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "]";
}
template <typename F, typename S>
ostream &operator<<(ostream &os, const map<F, S> &v) {
  os << "[";
  typename map<F, S>::const_iterator it;
  for (it = v.begin(); it != v.end(); it++) {
    if (it != v.begin()) os << ", ";
    os << it->first << " = " << it->second;
  }
  return os << "]";
}
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
const long long N = 1e6 + 1, M = 1e5 + 5, mod = 1e9 + 7, MOD = 1e9 + 7,
                inf = 5e18, MAX = 2e5;
string alphabet = "abcdefghijklmnopqrstuvwxyz",
       capital = "ABCDEFGHIJKLMNOPQRSTUVWXYZ", dig = "0123456789";
vector<bool> taken(N, false);
vector<int> ar;
void solve(int tt) {
  int n, i, h, j, k, m, a, b;
  cin >> n;
  int sm = 0;
  for (int i = 1; i <= n; i++) {
    cin >> a;
    ar.push_back(a);
    taken[a] = true;
    sm += a - 1;
  }
  vector<int> ans;
  int cnt = 0;
  for (int i = 0; i < n; i++) {
    int cur = ar[i];
    if (!taken[N - cur])
      ans.push_back(N - cur);
    else
      ++cnt;
    taken[N - cur] = true;
  }
  for (int i = 1; i < N && cnt > 0; i++) {
    if (taken[i]) continue;
    int now = N - i;
    if (!taken[now]) {
      taken[i] = taken[now] = true;
      ans.push_back(i);
      ans.push_back(N - i);
      cnt -= 2;
    }
  }
  cout << ans.size() << "\n";
  for (auto z : ans) {
    sm -= (N - z - 1);
    cout << z << " ";
  }
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long i;
  long long T = 1, K;
  for (auto blockTime = make_pair(chrono::high_resolution_clock::now(), true);
       blockTime.second;
       fprintf(stderr, "%s: %d ms\n", "Exec Time : ",
               (int)chrono::duration_cast<chrono::milliseconds>(
                   chrono::high_resolution_clock::now() - blockTime.first)
                   .count()),
            fflush(stderr), blockTime.second = false) {
    long long x = 1;
    while (x <= T) {
      solve(x);
      x++;
    }
  }
  return 0;
}
