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