#include <bits/stdc++.h>
using namespace std;
bool isPrime(long long n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (long long i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
bool prime[100005];
void seive() {
  memset(prime, 1, sizeof(prime));
  prime[0] = 0;
  prime[1] = 0;
  for (long long i = 2; i * i <= 100000; i++) {
    if (prime[i] == 1) {
      for (long long j = i * i; j <= 100000; j += i) prime[j] = 0;
    }
  }
}
long long power(long long a, long long b) {
  long long ans = 1;
  while (b > 0) {
    if (b % 2 == 1) ans = (ans % 1000000007 * a % 1000000007) % 1000000007;
    a = (a * a) % 1000000007;
    b = b / 2;
  }
  return ans;
}
void solve() {
  long long n;
  cin >> n;
  if (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 {
    if (n % 2 == 0) {
      cout << n << endl;
      for (int i = 1; i <= n / 2; i++) cout << i << " " << i + n / 2 << " ";
    } else {
      cout << n << endl;
      for (int i = 1; i <= n / 2; i++)
        cout << i << " " << i + (n + 1) / 2 << " ";
      cout << (n + 1) / 2;
    }
  }
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  bool codechef = 0;
  long long t = 1;
  if (codechef) cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
