#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  if (n == 1 || n == 2) {
    cout << "1" << endl;
    cout << "1" << endl;
    return 0;
  }
  if (n == 3) {
    cout << "2" << endl;
    cout << "1"
         << " "
         << "3" << endl;
    return 0;
  }
  cout << n << endl;
  for (int i = 2; i <= n; i += 2) {
    cout << i << " ";
  }
  for (int i = 1; i <= n; i += 2) {
    cout << i << " ";
  }
  cout << endl;
}
