#include<stdio.h>
#include<bitset>
using namespace std;
bitset <2000000> a;
int n,i,j,jum,nr;
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);jum=n>>1;
	for(i=3;i<=n;i+=2)
	{
		if(a[i>>1]) continue;
		for(j=i+(i>>1);j<=jum;j+=i)
			a[j]=1;
		nr++;
	}
	printf("%d\n",nr+1);
	return 0;
}