#include <stdio.h>

int n, sol[1005], cnt, nr;
char ciur[2000002];

void erat()
{
	int i, j;
	for (i = 4; i <= n; i += 2) ciur[i] = 1;
	nr = 1;
	for (i = 3; i <= n; i += 2)
		if (!ciur[i]) { for (j = 2; i * j <= n; j++) ciur[i * j] = 1; nr++;}
	
}

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	erat();	
	
	printf("%d\n",nr);
	return 0;
}