#include <bits/stdc++.h>
using namespace std;
long long gcd(long long a, long long b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
long long mod(long long a, long long b) {
  if (a > b)
    return (a - b);
  else
    return (b - a);
}
double distance(long long x1, long long y1, long long x2, long long y2) {
  return sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2) * 1.0);
}
long long fact(long long n) {
  long long res = 1;
  for (long long i = 2; i <= n; i++) res = res * i;
  return res;
}
long long nCr(long long n, long long r) {
  return fact(n) / (fact(r) * fact(n - r));
}
bool isPerfectSquare(long double x) {
  long double sr = sqrt(x);
  return ((sr - floor(sr)) == 0);
}
bool isPrime(long long n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (long long i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
long long maxSum(long long arr[], long long n, long long k) {
  if (n < k) {
    cout << "Invalid";
    return -1;
  }
  long long res = 0;
  for (long long i = 0; i < k; i++) res += arr[i];
  long long curr_sum = res;
  for (long long i = k; i < n; i++) {
    curr_sum += arr[i] - arr[i - k];
    res = max(res, curr_sum);
  }
  return res;
}
class people {
  string name;
  string gender;

 public:
};
signed main() {
  ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
  long long n;
  cin >> n;
  long long arr[n];
  for (long long i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  vector<long long> v;
  for (long long i = 0; i < n; i++) {
    if (i <= 1) {
      v.push_back(arr[i]);
    } else {
      if (arr[i] != arr[i - 2]) v.push_back(arr[i]);
    }
  }
  long long maxi = *max_element(v.begin(), v.end());
  long long cnt = count(v.begin(), v.end(), maxi);
  if (cnt > 1) {
    v.pop_back();
  }
  vector<long long> v1(v.size());
  for (long long j = 0, k = 0; j < v.size(); k++, j++) {
    v1[k] = v[j];
    j++;
    if (j < v.size()) {
      v1[v.size() - 1 - k] = v[j];
    }
  }
  cout << v.size() << "\n";
  for (long long i = 0; i < v1.size(); i++) cout << v1[i] << " ";
  return 0;
}
