#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 = n - 1; i > 0; i -= 2) {
      cout << i << ' ';
    }
    for (int i = n; i > 0; i -= 2) {
      cout << i << ' ';
    }
  }
}
