#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;
    cout << "1 3";
  } else if (n == 4) {
    cout << 4 << endl;
    cout << "3 1 4 2";
  } 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 << " ";
    }
  }
}
