#include<stdio.h>

char a[2000001];

int ciuruire(int n)
{
	int i,j;
	int s=0;
	for(i=2;i<=1420&&(i<=n);++i)
	if(a[i] == 0)
	{
		s++;
		for(j=i*i;j<=n;j += i)
		{
			a[j] = i;
		}
	}
	for(;i<=n;i++)
	if(a[i] == 0)
	s++;
	return s;
}

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