#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e18 + 9;
const long long mod = 1e9 + 7;
const long long maxn = 2e5 + 8;
long long n, m;
void solve() {
  long long i, j;
  cin >> n;
  if (n <= 2) return (void)(cout << "1\n1" << endl);
  if (n == 3) return (void)(cout << "2\n1 3" << endl);
  if (n == 4) return (void)(cout << "4\n2 4 1 3" << endl);
  if (n == 5) return (void)(cout << "5\n1 4 2 5 3" << endl);
  cout << n << endl;
  if (n & 1) cout << n << " ";
  for (i = 1; i <= n / 2; i++)
    cout << i << " " << i + n / 2 << " \n"[i == n / 2];
}
signed main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  long long t = 1;
  while (t--) solve();
  return 0;
}
