#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  if (n == 1 || n == 2) {
    cout << "1" << endl << "1 ";
  } else if (n == 3) {
    cout << "2" << endl << "1 3";
  } else if (n == 4) {
    cout << "4" << endl << "2 4 1 3";
  } else {
    cout << n << endl;
    for (int i = 1; i <= n; i = i + 2) {
      cout << i << " ";
    }
    for (int i = 2; i <= n; i = i + 2) {
      cout << i << " ";
    }
  }
  return 0;
}
