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