#include <stdio.h>

int N, cnt;
char prim[2000005];

int main(void)
{
	int i, j;

	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	scanf("%d", &N);
	for (i = 2; i <= N; ++i)
		prim[i] = 1;
	for (i = 2; i <= N; ++i)
	if (prim[i])
	{
		++cnt;
		for (j = i + i; j <= N; j += i)
			prim[j] = 0;
	}

	printf("%d\n", cnt);

	return 0;