#include <bits/stdc++.h>
std::mt19937 rng(
    (int)std::chrono::steady_clock::now().time_since_epoch().count());
using namespace std;
long long mod = (1000000007LL);
inline long long Mod(long long a, long long b) { return (a % b); }
inline long long poww(long long a, long long b) {
  long long res = 1;
  while (b > 0) {
    if (b & 1) res = (res * a) % mod;
    a = (a * a) % mod;
    b >>= 1;
  }
  return res;
}
long long gcd(long long a, long long b) {
  while (b) {
    a %= b, swap(a, b);
  }
  return a;
}
void read(vector<int> &w, int n) {
  w.resize(n);
  for (int i = 0; i < n; i++) cin >> w[i];
}
void print(vector<int> &w) {
  for (int i = 0; i < (int)(w).size(); i++) {
    if (i == (int)(w).size() - 1)
      cout << w[i] << "\n";
    else
      cout << w[i] << " ";
  }
}
int prodmod(vector<int> w);
int summod(vector<int> w);
int n, m, q, k, v[300050], ans;
pair<int, int> w[300050];
string second;
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int q = 1;
  vector<int> opt;
  while (q--) {
    int n;
    cin >> n;
    vector<int> val;
    read(val, n);
    sort(begin(val), end(val));
    int ini = 0, fim = n, mid, best = -1;
    while (fim >= ini) {
      mid = (ini + fim) / 2;
      vector<int> L, R;
      bool can = true;
      for (int i = 0; i < mid; i++) L.push_back(val[i]);
      for (int i = n - 1; (int)(R).size() < mid + 1; i--) {
        if (i < 0 or i < mid) can = false;
        R.push_back(val[i]);
      }
      reverse(begin(R), end(R));
      if (!can)
        fim = mid - 1;
      else {
        vector<int> good;
        good.push_back(R[0]);
        for (int i = 0; i < mid; i++) {
          good.push_back(L[i]);
          good.push_back(R[i + 1]);
        }
        for (int i = 0; i < (int)(good).size() - 1; i++) {
          if (good[i] == good[i + 1]) can = false;
        }
        if (!can)
          fim = mid - 1;
        else
          ini = mid + 1, best = mid, opt = good;
      }
    }
    cout << best << "\n";
    for (int i = mid; (int)(opt).size() < n; i++) opt.push_back(val[i]);
    print(opt);
  }
}
int summod(vector<int> w) {
  int curr = 0;
  for (int i = 0; i < (int)(w).size(); i++) {
    curr = (curr + w[i]) % mod;
    if (curr < 0) curr += mod;
  }
  return curr;
}
int prodmod(vector<int> w) {
  int curr = 1;
  for (int i = 0; i < (int)(w).size(); i++) {
    if (w[i] >= mod) w[i] %= mod;
    curr = (curr * w[i]) % mod;
    if (curr < 0) curr += mod;
  }
  return curr;
}
