#include <bits/stdc++.h>
void swap(int* n, int* m) {
  int t;
  t = *n;
  *n = *m;
  *m = t;
}
int main() {
  int n;
  scanf("%d", &n);
  if (n == 1 || n == 2) {
    printf("1\n1");
    return 0;
  } else if (n == 3) {
    printf("2\n1 3");
    return 0;
  } else if (n == 4) {
    printf("4\n3 1 4 2");
    return 0;
  } else if (n == 5) {
    printf("5\n3 1 4 2 5");
    return 0;
  } else if (n >= 6) {
    int* wu = (int*)malloc(n * sizeof(int));
    int x = n % 6, y = n - x;
    for (int i = 0; i < n; i++) wu[i] = i + 1;
    for (int j = 0; j < y; j = j + 6) {
      swap(&wu[j + 1], &wu[j + 4]);
      swap(&wu[j + 3], &wu[j + 5]);
    }
    if (x == 2 || x == 3)
      swap(&wu[y + 1], &wu[0]);
    else if (x == 4 || x == 5) {
      swap(&wu[y + 1], &wu[0]);
      swap(&wu[y + 3], &wu[1]);
    }
    printf("%d\n", n);
    for (int i = 0; i < n; i++) {
      printf("%d ", wu[i]);
    }
    free(wu);
  }
  return 0;
}
