#include <stdio.h>

const int N_MAX = 5010;

int main()
{
	freopen("sortare.in", "r", stdin);
#ifndef _SCREEN_
	freopen("sortare.out", "w", stdout);
#endif

	int N;
	scanf("%d\n", &N);

	if (N % 2 == 1) printf("%d\n", N / 2 + 1);
	else printf("%d\n", N / 2);
	for (int i = 1; i <= N; i ++) {
		printf("%d ", i);
	}
	printf("\n");

	return 0;
}