#include <cstdio>
using namespace std;

const int N=2000005;
int c[N],nr;

void ciur(int n)
{
	int i,j;
	for(i=2;i*i<n;i++)
		if(!c[i])
			for(j=i*i;j<n;j+=i)
				c[j]=true;
	for(i=2;i<n;++i)
		if(!c[i])
			nr++;
}

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