#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
const long long N = 1e5;
const long long inf = 1e18;
long long Pow(long long a, long long b) {
  a = a % mod;
  long long res = 1;
  while (b) {
    if (b & 1) res = (res * a) % mod;
    a = (a * a) % mod;
    b >>= 1;
  }
  return (res % mod);
}
long long Inv(long long a, long long m) { return Pow(a, m - 2); }
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long lcm(long long a, long long b) { return (a * b) / gcd(a, b); }
void solve() {
  long long n;
  cin >> n;
  vector<long long> v1, v2;
  for (long long i = 1; i <= n; i++) {
    if (i & 1)
      v1.push_back(i);
    else
      v2.push_back(i);
  }
  cout << v2.size() + v1.size() + v2.size() << "\n";
  for (long long i = 0; i < v2.size(); i++) cout << v2[i] << " ";
  for (long long i = 0; i < v1.size(); i++) cout << v1[i] << " ";
  for (long long i = 0; i < v2.size(); i++) cout << v2[i] << " ";
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long t = 1;
  for (long long i = 1; i <= t; i++) solve();
  return 0;
}
