#include <bits/stdc++.h>
using namespace std;
template <class T>
inline T bigmod(T p, T e, T M) {
  long long int ret = 1;
  for (; e > 0; e >>= 1) {
    if (e & 1) ret = (ret * p) % M;
    p = (p * p) % M;
  }
  return (T)ret;
}
template <class T>
inline T bpow(T p, T e) {
  long long int ret = 1;
  for (; e > 0; e >>= 1) {
    if (e & 1) ret = (ret * p);
    p = (p * p);
  }
  return (T)ret;
}
template <class T>
inline T modinverse(T a, T M) {
  return bigmod(a, M - 2, M);
}
template <class T>
inline T gcd(T a, T b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
vector<int> v;
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 2; i <= n; i += 2) {
    v.push_back(i);
  }
  for (int k = 1; k <= n; k += 2) {
    v.push_back(k);
  }
  for (int i = 2; i <= n; i += 2) {
    v.push_back(i);
  }
  printf("%d\n", v.size());
  for (int i = 0; i < v.size(); i++) {
    if (i > 0) printf(" ");
    printf("%d", v[i]);
  }
  printf("\n");
  return 0;
}
